dockerでBASIC:docker(116)

dockerでBASICを使おうとGCCで起動

```
$ docker run -it gcc /bin/bash
```
basicを検索

```
# apt update; apt -y upgrade; apt install man
# apt search basic
Sorting... Done
Full Text Search... Done
acheck-rules/stable 0.3.3 all
  Basic rules for acheck

bwbasic/stable 2.20pl2-11+b2 amd64
  Bywater BASIC Interpreter

yabasic/stable 1:2.82.0-1 amd64
  Yet Another BASIC interpreter

# apt install yabasic
# man yabasic
yabasic(1)                   General Commands Manual                   yabasic(1)

NAME
       yabasic - yet another Basic

SYNOPSIS
       yabasic [OPTIONS] [FILENAME [ARGUMENTS]]

DESCRIPTION
       Yabasic  implements  the most common and simple elements of the basic lan-
       guage. It comes with goto/gosub, with various  loops,  with  user  defined
       subroutines  and  libraries.  Yabasic  does  simple graphics and printing.
       Yabasic runs under Unix and Windows, it is small, open source and free.

       This man-page is derived from yabasic.htm, which too should  be  installed
       on your system; per default in

       /usr/local/share/applications/yabasic/yabasic.htm.

       The same information can also be found on www.yabasic.de

       Here is its content:

        Yabasic

        ----------------------------------------------------------------------------
---

        Table of Contents

        1. Introduction

            About this document
            About yabasic

        2. The yabasic-program under Windows

            Starting yabasic
            Options
            The context Menu

        3. The yabasic-program under Unix

            Starting yabasic
            Options
            Setting defaults

        4. Command line options of yabasic
        5. Some features of yabasic, explained by topic

            print, input and others
            Control statements: loops, if and switch
            Drawing and painting
            Reading from and writing to files
            Subroutines and Libraries
            String processing
            Arithmetic and numbers
            Data and such
            Other interesting commands.

        6. All commands and functions of yabasic listed by topic

            Number processing and conversion
            Conditions and control structures
            Data keeping and processing
            String processing
            File operations and printing
            Subroutines and libraries
            Other commands
            Graphics and printing

        7. All commands and functions of yabasic grouped alphabetically

            A
            B
            C
            D
            E
            F
            G
            H
            I
            L
            M
            N
            O
            P
            R
            S
            T
            U
            V
            W
            X
            Special characters
            Reserved Words

        8. Some general concepts and terms

            Logical shortcuts
            Conditions and expressions
            References on arrays
            Specifying Filenames under Windows
            Escape-sequences
            Creating a standalone program from your yabasic-program

        9. A few example programs

            A very simple program
            The demo of yabasic

        10. The Copyright of yabasic

        Chapter 1. Introduction

        About this document
        About yabasic

        About this document

        This document describes yabasic. You will find information about the yabasic
        interpreter (the program yabasic under Unix or yabasic.exe under Windows) as
        well as the language (which is, of course, a sort of basic) itself.

        This document applies to version 2.82 of yabasic

        However, this document does not contain the latest news about yabasic or a F
AQ.
        As such information tends to change rapidly, it is presented online only at
        www.yabasic.de.

        Although basic has its reputation as a language for beginning programmers, t
his
        is not an introduction to programming at large. Rather this text assumes, th
at
        the reader has some (moderate) experience with writing and starting computer
        programs.

        About yabasic

        yabasic is a traditional basic interpreter. It understands most of the typic
al
        basic-constructs, like goto, gosub, line numbers, read, data or
        string-variables with a trailing '$'. But on the other hand, yabasic impleme
nts
        some more advanced programming-constructs like subroutines or libraries (but
        not objects). yabasic works much the same under Unix and Windows.

        yabasic puts emphasis on giving results quickly and easily; therefore simple
        commands are provided to open a graphic window, print the graphics or contro
l
        the console screen and get keyboard or mouse information. The example below
        opens a window, draws a circle and prints the graphic:

        open window 100,100
        open printer
        circle 50,50,40
        text 10,50,"Press any key to get a printout"
        clear screen
        inkey$
        close printer
        close window

        This example has fewer lines, than it would have in many other programming
        languages. In the end however yabasic lacks behind more advanced and modern
        programming languages like C++ or Java. But as far as it goes it tends to gi
ve
        you results more quickly and easily.

        Chapter 2. The yabasic-program under Windows

        Starting yabasic
        Options
        The context Menu

        Starting yabasic

        Once, yabasic has been set up correctly, there are three ways to start it:

         1. Right click on your desktop: The desktop menu appears with a submenu nam
ed
            new. From this submenu choose yabasic. This will create a new icon on yo
ur
            desktop. If you right click on this icon, its context menu will appear;
            choose Execute to execute the program.

         2. As a variant of the way described above, you may simply create a file wi
th
            the ending .yab (e.g. with your favorite editor). Everything else then
            works as described above.

         3. From the start-menu: Choose yabasic from your start-menu. A console-wind
ow
            will open and you will be asked to type in your program. Once you are
            finished, you need to type return twice, and yabasic will parse and exec
ute
            your program.

            Note

            This is not the preferred way of starting yabasic ! Simply because the
            program, that you have typed, can not be saved and will be lost inevitab
ly
            ! There is no such thing as a save-command and therefore no way to conse
rve
            the program, that you have typed. This mode is only intended for quick
            hacks, and short programs.

        Options

        Under Windows yabasic will mostly be invoked by double-clicking on an
        appropriate icon; this way you do not have a chance to specify any of the
        command line options below. However, advanced users may change the librarypa
th
        in the registry, which has the same effect as specifying it as an option on 
the
        command line.

        See the chapter on options for a complete list of all options, either on Uni
x
        or Windows.

        The context Menu

        Like every other icon under Windows, the icon of every yabasic-program has a
        context menu offering the most frequent operations, that may be applied to a
        yabasic-program.

        Execute

            This will invoke yabasic to execute your program. The same happens, if y
ou
            double click on the icon.

        Edit

            notepad will be invoked, allowing you to edit your program.

        View docu

            This will present the embedded documentation of your program. Embedded
            documentation is created with the special comment doc.

        Chapter 3. The yabasic-program under Unix

        Starting yabasic
        Options
        Setting defaults

        Starting yabasic

        If your system administrator (vulgo root) has installed yabasic correctly,
        there are three ways to start it:

         1. You may use your favorite editor (emacs, vi ?) to put your program into 
a
            file (e.g. foo). Make sure that the very first line starts with the
            characters '#!' followed by the full pathname of yabasic (e.g. '#!/usr/
            local/bin/yabasic'). This she-bang-line ensures, that your Unix will inv
oke
            yabasic to execute your program (see also the entry for the hash
            -character). Moreover, you will need to change the permissions of your
            yabasic-program foo, e.g. chmod u+x foo. After that you may invoke yabas
ic
            to invoke your program by simply typing foo (without even mentioning
            yabasic). However, if your PATH-variable does not contain a single dot
            ('.') you will have to type the full pathname of your program: e.g. /hom
e/
            ihm/foo (or at least ./foo).

         2. Save your program into a file (e.g. foo) and type yabasic foo. This
            assumes, that the directory, where yabasic resides, is contained within
            your PATH-variable.

         3. Finally your may simply type yabasic (maybe it will be necessary to incl
ude
            its full pathname). This will make yabasic come up and you will be asked
 to
            type in your program. Once you are finished, you need to type return twi
ce,
            and yabasic will parse and execute your program.

            Note

            This is not the preferred way of starting yabasic ! Simply because the
            program, that you have typed, can not be saved and will be lost inevitab
ly
            ! There is no such thing as a save-command and therefore no way to conse
rve
            the program, that you have typed. This mode is only intended for quick
            hacks, and short programs, i.e. for using yabasic as some sort of fancy
            desktop calculator.

        Options

        yabasic accepts a number of options on the command line.

        See chapter on options for a complete list of all options, either on Unix or
        Windows.

        Setting defaults

        If you want to set some options once for all, you may put them into your
        X-Windows resource file. This is usually the file .Xresources or some such
        within your home directory (type man X for details).

        Here is a sample section, which may appear within this file:

        yabasic*foreground: blue
        yabasic*background: gold
        yabasic*geometry: +10+10
        yabasic*font: 9x15

        This will set the foreground color of the graphic-window to blue and the
     background color to gold. The window will appear at position 10,10 and the text
        font will be 9x15.

        Chapter 4. Command line options of yabasic

      Here are the options, that yabasic accepts on the command line (both under Unix
        and Windows).

        All the options below may be abbreviated (and one hyphen may be dropped), as
        long as the abbreviation does not become ambiguous. For example, you may write
        -e instead of --execute.

        --help or -?

            Prints a short help message, which itself describes two further
            help-options.

        --version

            Prints the version of yabasic.

        --infolevel INFOLEVEL

       Change the infolevel of yabasic, where INFOLEVEL can be one of debug, note,
            warning, error, fatal and bison (the default is warning). This option
            changes the amount of debugging-information yabasic produces. However,
            normally only the author of yabasic (me !) would want to change this.

        --execute A-PROGRAM-AS-A-SINGLE-STRING

            With this option you may specify some yabasic-code to be executed right
          away. This is useful for very short programs, which you do not want to save
            to a file. If this option is given, yabasic will not read any code from a
            file. E.g.

            yabasic -e 'for a=1 to 10:print a*a:next a'

            prints the square numbers from 1 to 10.

        --bind NAME-OF-STANDALONE-PROGRAM

            Create a standalone program (whose name is specified by
            NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on
            the command line. See the section about creating a standalone-program for
            details.

        --geometry +X-POSITION+Y-POSITION

            Sets the position of the graphic window, that is opened by open window (the
            size of this window, of course, is specified within the open
            window-command). An example would be -geometry +20+10, which would place
            the graphic window 10 pixels below the upper border and 20 pixels right of
            the left border of the screen. This value cannot be changed, once yabasic
            has been started.

        -fg FOREGROUND-COLOR or --foreground FOREGROUND-COLOR

            Unix only. Define the foreground color for the graphics-window (that will
            be opened with open window). The usual X11 color names, like red, green,?
            are accepted. This value cannot be changed, once yabasic has been started.

        -bg BACKGROUND-COLOR or --background BACKGROUND-COLOR

            Unix only. Define the background color for the graphics-window. The usual
            X11 color names are accepted. This value cannot be changed, once yabasic
            has been started.

        --display X11-DISPLAY-SPECIFICATION

           Unix only. Specify the display, where the graphics window of yabasic should
            appear. Normally this value will be already present within the environment
            variable DISPLAY.

        --font NAME-OF-FONT

            Under Unix. Name of the font, which will be used for text within the
            graphics window.

        --font NAME-OF-FONT

            Under Windows. Name of the font, which will be used for graphic-text; can
            be any of decorative, dontcare, modern, roman, script, swiss. You may
            append a fontsize (measured in pixels) to any of those fontnames; for
            example -font swiss30 chooses a swiss-type font with a size of 30 pixels
.

        --docu NAME-OF-A-PROGRAM

            Print the embedded documentation of the named program. The embedded
           documentation of a program consists of all the comments within the program,
            which start with the special keyword doc. This documentation can also be
            seen by choosing the corresponding entry from the context-menu of any
            yabasic-program.

        --check

            Check for possible compatibility problems within your yabasic-program. E
.g.
            this option reports, if you are using a function, that has recently
            changed.

        --librarypath DIRECTORY-WITH-LIBRARIES

         Change the directory, wherein libraries will be searched and imported (with
            the import-command). See also import for more information about the way,
            libraries are searched.

        --

            Do not try to parse any further options; rather pass the subsequent words
            from the commandline to yabasic.

        Chapter 5. Some features of yabasic, explained by topic

        print, input and others
        Control statements: loops, if and switch
        Drawing and painting
        Reading from and writing to files
        Subroutines and Libraries
        String processing
        Arithmetic and numbers
        Data and such
        Other interesting commands.

      This chapter has sections for some of the major features of yabasic and names a
        few commands related with each area. So, depending on your interest, you find
        the most important commands of this area named; the other commands from this
        area may then be discovered through the links in the see also-section.

        print, input and others

        The print-command is used to put text on the text screen. Here, the term text
        screen stands for your terminal (under Unix) or the console window (under
        Windows).

        At the bottom line, print simply outputs its argument to the text window.
        However, once you have called clear screen you may use advanced features like
        printing colors or copying areas of text with getscreen$ or putscreen.

        You may ask the user for input with the input-command; use inkey$ to get each
        key as soon as it is pressed.

        Control statements: loops, if and switch

      Of course, yabasic has the goto- and gosub-statements; you may go to a label or
        a line number (which is just a special kind of label). goto, despite its bad
        reputation ([goto considered harmful]), has still its good uses; however in
       many cases you are probably better off with loops like repeat-until, while-wend
        or do-loop; you may leave any of these loops with the break-statement or start
        the next iteration immediately with continue.

        Decisions can be made with the if-statement, which comes either in a short and
        a long form. The short form has no then-keyword and extends up to the end of
        the line. The long form extends up to the final endif and may use some of the
        keywords then (which introduces the long form), else or elsif.

        If you want to test the result of an expression against many different values,
        you should probably use the switch-statement.

        Drawing and painting

        You need to call open window before you may draw anything with either line,
        circle, rectangle or triangle; all of these statements may be decorated with
        clear or fill. If you want to change the colour for drawing, use colour. Note
        however, that there can only be a single window open at any given moment in
        time.

        Everything you have drawn can be send to your printer too, if you use the open
        printer command.

        To allow for some (very) limited version of animated graphics, yabasic offers
        the commands getbit$ and putbit, which retrieve rectangular regions from the
        graphics-window into a string or vice versa.

        If you want to sense mouse-clicks, you may use the inkey$-function.

        Reading from and writing to files

        Before you may read or write a file, you need to open it; once you are done,
        you should close it. Each open file is designated by a simple number, which
        might be stored within a variable and must be supplied if you want to access
       the file. This is simply done by putting a hash ('#') followed by the number of
        the file after the keyword input (for reading from) or print (for writing to a
        file) respectively.

        If you need more control, you may consider reading and writing one byte at a
        time, using the multi-purpose commands peek and poke.

        Subroutines and Libraries

        The best way to break any yabasic-program into smaller, more manageable chunks
        are subroutines and libraries. They are yabasic's most advanced means of
        structuring a program.

        Subroutines are created with the command sub. they accept parameters and may
        return a value. Subroutines can be called much like any builtin function of
        yabasic; therefore they allow one to extend the language itself.

     Once you have created a set of related subroutines and you feel that they could
        be useful in other programs too, you may collect them into a library. Such a
        library is contained within a separate file and may be included in any of your
        programs, using the keyword import, which see.

        String processing

        yabasic has a set of functions to extract parts from a string: left$, mid$ and
       right$. Note, that all of them can be assigned to, i.e. they may change part of
        a string.

        If you want to split a string into tokens you should use the functions token
 or
        split.

        Some functions are handy for normalizing a string: upper$ and lower$ convert
 a
        string to all upper or lower case respectively, whereas chomp$ cuts of any
        trailing newline character, but only if present.

        chr$ and str$ convert a string into a number, both in different ways.

        To analyze a string use instr (finding one string within the other) or glob
        (testing a string against a simple pattern).

        To concatenate strings use the operator + like in a$ + b$.

        You may also see the complete list of a string processing functions.

        Arithmetic and numbers

        Yabasic handles numbers and arithmetic: You may calculate trigonometric
        functions like sin or atan, or logarithms (with log). Bitwise operations, li
ke
        and or or are available as well min or max (calculate the minimum or maximum
 of
        its argument) or mod or int (reminder of a division or integer part or a
        number).

        Conversion between numerical bases can be done with hex$ and dec. And you ma
y
        write hexadecimal constants in the usual way, e.g.

        print 0xff

        . All calculations in yabasic are done with double precision.

        Data and such

        You may store data within your program within data-statements; during execut
ion
        you will probably want to read it into arrays, which must have been dimed
        before.

        Other interesting commands.

          * Yabasic programs may start other programs with the commands system and
            system$.

          * peek and poke allow one to get and set internal information; either for 
the
            operating system (i.e. Unix or Windows) or yabasic itself.

          * The current time or date can be retrieved with (guess what !) time$ and
            date$.

        Chapter 6. All commands and functions of yabasic listed by topic

        Number processing and conversion
        Conditions and control structures
        Data keeping and processing
        String processing
        File operations and printing
        Subroutines and libraries
        Other commands
        Graphics and printing

        Number processing and conversion

        abs()
            returns the absolute value of its numeric argument
        acos()
            returns the arcus cosine of its numeric argument
        and()
            the bitwise arithmetic and
        asin()
            returns the arcus sine of its numeric argument
        atan()
            returns the arctangent of its numeric argument
        bin$()
           converts a number into a sequence of binary digits
        cos()
            return the cosine of its single argument
        dec()
            convert a base 2 or base 16 number into decimal form
        eor()
            compute the bitwise exclusive or of its two arguments
        euler
            another name for the constant 2.71828182864
        exp()
            compute the exponential function of its single argument
        frac()
            return the fractional part of its numeric argument
        int()
            return the integer part of its single numeric argument
        ceil()
            return the smallest integral number, that is greater or equal than i
ts
            argument
        floor()
            return the largest integral number, that is smaller or equal than it
s
            argument
        log()
            compute the natural logarithm
        max()
            return the larger of its two arguments
        min()
            return the smaller of its two arguments
        mod
            compute the remainder of a division
        or()
            arithmetic or, used for bit-operations
        pi
            a constant with the value 3.14159
        ran()
            return a random number
        sig()
            return the sign of its argument
        sin()
            return the sine of its single argument
        sqr()
            compute the square of its argument
        sqrt()
            compute the square root of its argument
        tan()
            return the tangent of its argument
        xor()
            compute the exclusive or
        ** or ^
            raise its first argument to the power of its second

        Conditions and control structures

        and
            logical and, used in conditions
        break
            breaks out of a switch statement or a loop
        case
            mark the different cases within a switch-statement
        continue
            start the next iteration of a for-, do-, repeat- or while-loop
        default
            mark the default-branch within a switch-statement
        do
            start a (conditionless) do-loop
        else
            mark an alternative within an if-statement
        elsif
            starts an alternate condition within an if-statement
        end
            terminate your program
        endif
            ends an if-statement
        false
            a constant with the value of 0
        fi
            another name for endif
        for
            starts a for-loop
        gosub
            continue execution at another point within your program (and return 
later)
        goto
            continue execution at another point within your program (and never c
ome
            back)
        if
            evaluate a condition and execute statements or not, depending on the
 result
        label
            mark a specific location within your program for goto, gosub or rest
ore
        loop
            marks the end of an infinite loop
        next
            mark the end of a for loop
        not
            negate an expression; can be written as !
        on gosub
            jump to one of multiple gosub-targets
        on goto
            jump to one of many goto-targets
        on interrupt
            change reaction on keyboard interrupts
        logical or
            logical or, used in conditions
        pause
            pause, sleep, wait for the specified number of seconds
        repeat
            start a repeat-loop
        return
            return from a subroutine or a gosub
        sleep
            pause, sleep, wait for the specified number of seconds
        switch
            select one of many alternatives depending on a value
        then
            tell the long from the short form of the if-statement
        true
            a constant with the value of 1
        until
            end a repeat-loop
        wait
            pause, sleep, wait for the specified number of seconds
        wend
            end a while-loop
        while
            start a while-loop
        :
            separate commands from each other

        Data keeping and processing

        arraydim()
            returns the dimension of the array, which is passed as an array refe
rence
        arraysize()
            returns the size of a dimension of an array
        data
            introduces a list of data-items
        dim
            create an array prior to its first use
        read
            read data from data-statements
        redim
            create an array prior to its first use. A synonym for dim
        restore
            reposition the data-pointer

        String processing

        asc()
            accepts a string and returns the position of its first character wit
hin the
            ascii charset
        chomp$()
            Chop of the trailing newline of its string-argument; if the string d
oes not
            end in a newline, the string is returned unchanged
        chr$()
            accepts a number and returns the character at this position within t
he
            ascii charset
        glob()
            check if a string matches a simple pattern
        hex$()
            convert a number into hexadecimal
        instr()
            searches its second argument within the first; returns its position 
if
            found
        left$()
            return (or change) left end of a string
        len()
            return the length of a string
        lower$()
            convert a string to lower case
        ltrim$()
            trim spaces at the left end of a string
        mid$()
            return (or change) characters from within a string
        right$()
            return (or change) the right end of a string
        split()
            split a string into many strings
        str$()
            convert a number into a string
        token()
            split a string into multiple strings
        trim$()
            remove leading and trailing spaces from its argument
        upper$()
            convert a string to upper case
        val()
            converts a string to a number

        File operations and printing

        at()
            can be used in the print-command to place the output at a specified
            position
        beep
            ring the bell within your computer; a synonym for bell
        bell
            ring the bell within your computer (just as beep)
        clear screen
            erases the text window
        close
            close a file, which has been opened before
        close printer
            stops printing of graphics
        print color
            print with color
        print colour
            see print color
        eof
            check, if an open file contains data
        getscreen$()
            returns a string representing a rectangular section of the text term
inal
        inkey$
            wait, until a key is pressed
        input
            read input from the user (or from a file) and assign it to a variabl
e
        line input
            read in a whole line of text and assign it to a variable
        open
            open a file
        open printer
            open printer for printing graphics
        print
            Write to terminal or file
        putscreen
            draw a rectangle of characters into the text terminal
        reverse
            print reverse (background and foreground colors exchanged)
        screen
            as clear screen clears the text window
        seek()
            change the position within an open file
        tell
            get the current position within an open file
        using
            Specify the format for printing a number
        #
            either a comment or a marker for a file-number
        @
            synonymous to at
        ;
            suppress the implicit newline after a print-statement

        Subroutines and libraries

        end sub
            ends a subroutine definition
        export
            mark a function as globally visible
        import
            import a library
        local
            mark a variable as local to a subroutine
        numparams
            return the number of parameters, that have been passed to a subrouti
ne
        return
            return from a subroutine or a gosub
        static
            preserves the value of a variable between calls to a subroutine
        step
            specifies the increment step in a for-loop
        sub
            declare a user defined subroutine

        Other commands

        bind()
            Binds a yabasic-program and the yabasic-interpreter together into a
            standalone program.
        compile
            compile a string with yabasic-code on the fly
        date$
            returns a string with various components of the current date
        doc
            special comment, which might be retrieved by the program itself
        docu$
            special array, containing the contents of all docu-statement within 
the
            program
        error
            raise an error and terminate your program
        execute$()
            execute a user defined subroutine, which must return a string
        execute()
            execute a user defined subroutine, which must return a number
        exit
            terminate your program
        pause
            pause, sleep, wait for the specified number of seconds
        peek
            retrieve various internal information
        peek$
            retrieve various internal string-information
        poke
            change selected internals of yabasic
        rem
            start a comment
        sleep
            pause, sleep, wait for the specified number of seconds
        system()
            hand a statement over to your operating system and return its exitco
de
        system$()
            hand a statement over to your operating system and return its output
        time$
            return a string containing the current time
        to
            this keyword appears as part of other statements
        wait
            pause, sleep, wait for the specified number of seconds
        //
            starts a comment
        :
            separate commands from each other

        Graphics and printing

        backcolor
            specify the colour for subsequent drawing of the background
        box
            draw a rectangle. A synonym for rectangle
        circle
            draws a circle in the graphic-window
        clear
            Erase circles, rectangles or triangless
        clear window
            clear the graphic window and begin a new page, if printing is under 
way
        close curve
            close a curve, that has been drawn by the line-command
        close window
            close the graphics-window
        colour
            specify the colour for subsequent drawing
        dot
            draw a dot in the graphic-window
        fill
            draw a filled circles, rectangles or triangles
        getbit$()
            return a string representing the bit pattern of a rectangle within t
he
            graphic window
        line
            draw a line
        mouseb
            extract the state of the mousebuttons from a string returned by inke
y$
        mousemod
            return the state of the modifier keys during a mouseclick
        mousex
            return the x-position of a mouseclick
        mousey
            return the y-position of a mouseclick
        new curve
            start a new curve, that will be drawn with the line-command
        open window
            open a graphic window
        putbit
            draw a rectangle of pixels into the graphic window
        rectangle
            draw a rectangle
        triangle
            draw a triangle
        text
            write text into your graphic-window
        window origin
            move the origin of a window

        Chapter 7. All commands and functions of yabasic grouped alphabetically

        A
        B
        C
        D
        E
        F
        G
        H
        I
        L
        M
        N
        O
        P
        R
        S
        T
        U
        V
        W
        X
        Special characters
        Reserved Words

        A

        abs() ? returns the absolute value of its numeric argument
        acos() ? returns the arcus cosine of its numeric argument
        and ? logical and, used in conditions
        and() ? the bitwise arithmetic and
        arraydim() ? returns the dimension of the array, which is passed as an a
rray
            reference
        arraysize() ? returns the size of a dimension of an array
        asc() ? accepts a string and returns the position of its first character
 within
            the ascii charset
        asin() ? returns the arcus sine of its numeric argument
        at() ? can be used in the print-command to place the output at a specifi
ed
            position
        atan() ? returns the arctangent of its numeric argument

        Name

        abs() ? returns the absolute value of its numeric argument

        Synopsis

        y=abs(x)

        Description

        If the argument of the abs-function is positive (e.g. 2) it is returned
        unchanged, if the argument is negative (e.g. -1) it is returned as a pos
itive
        value (e.g. 1).

        Example

        print abs(-2),abs(2)

        This example will print 2 2

        See also

        sig

        ------------------------------------------------------------------------
-------

        Name

        acos() ? returns the arcus cosine of its numeric argument

        Synopsis

        x=acos(angle)

        Description

        acos is the arcus cosine-function, i.e. the inverse of the cos-function.
 Or,
        more elaborate: It Returns the angle (in radians, not degrees !), which,
 fed to
        the cosine-function will produce the argument passed to the acos-functio
n.

        Example

        print acos(0.5),acos(cos(pi))

        This example will print 1.0472 3.14159 which are ?/3 and ? respectively.

        See also

        cos, asin

        ------------------------------------------------------------------------
-------

        Name

        and ? logical and, used in conditions

        Synopsis

        if (a and b) ?
        while (a and b) ?

        Description

        Used in conditions (e.g within if, while or until) to join two expressio
ns.
        Returns true, if and only if its left and right argument are both true a
nd
        false otherwise.

        Note, that logical shortcuts may take place.

        Example

        input "Please enter a number" a
        if (a>=1 and a<=9) print "your input is between 1 and 9"

        See also

        or,not

        ------------------------------------------------------------------------
-------

        Name

        and() ? the bitwise arithmetic and

        Synopsis

        x=and(a,b)

        Description

        Used to compute the bitwise and of both its argument. Both arguments are
        treated as binary numbers (i.e. a series of 0 and 1); a bit of the resul
ting
        value will then be 1, if both arguments have a 1 at this position in the
ir
        binary representation.

        Note, that both arguments are silently converted to integer values and t
hat
        negative numbers have their own binary representation and may lead to
        unexpected results when passed to and.

        Example

        print and(6,3)

        This will print 2. This result is clear, if you note, that the binary
        representation of 6 and 3 are 110 and 011 respectively; this will yield 
010 in
        binary representation or 2 as decimal.

        See also

        or, eor and not

        ------------------------------------------------------------------------
-------

        Name

        arraydim() ? returns the dimension of the array, which is passed as an a
rray
        reference

        Synopsis

        a=arraydim(b())

        Description

        If you apply the arraydim()-function on a one-dimensional array (i.e. a 
vector)
        it will return 1, on a two-dimensional array (i.e. a matrix) it will ret
urn 2,
        and so on.

        This is mostly used within subroutines, which expect an array among thei
r
        parameters. Such subroutines tend to use the arraydim-function to check,
 if the
        array which has been passed, has the right dimension. E.g. a subroutine 
to
        multiply two matrices may want to check, if it really is invoked with tw
o
        2-dimensional arrays.

        Example

        dim a(10,10),b(10)
        print arraydim(a()),arraydim(b())

        This will print 2 1, which are the dimension of the arrays a() and b(). 
You may
        check out the function arraysize for a full-fledged example.

        See also

        arraysize and dim.

        ------------------------------------------------------------------------
-------

        Name

        arraysize() ? returns the size of a dimension of an array

        Synopsis

        x=arraysize(a(),b)

        Description

        The arraysize-function computes the size of a specified dimension of a
        specified array. Here, size stands for the maximum number, that may be u
sed as
        an index for this array. The first argument to this function must be an
        reference to an array, the second one specifies, which of the multiple
        dimensions of the array should be taken to calculate the size.

        An Example involving subroutines: Let's say, an array has been declared 
as dim
        a(10,20) (that is a two-dimensional array or a matrix). If this array is
 passed
        as an array reference to a subroutine, this sub will not know, what sort
 of
        array has been passed. With the arraydim-function the sub will be able t
o find
        the dimension of the array, with the arraysize-function it will be able 
to find
        out the size of this array in its two dimensions, which will be 10 and 2
0
        respectively.

        Our sample array is two dimensional; if you envision it as a matrix this
 matrix
        has 10 lines and 20 columns (see the dim-statement above. To state it mo
re
        formally: The first dimension (lines) has a size of 10, the second dimen
sion
        (columns) has a size of 20; these numbers are those returned by arraysiz
e(a
        (),1) and arraysize(a(),2) respectively. Refer to the example below for 
a
        typical usage.

        Example

        rem
        rem  This program adds two matrices elementwise.
        rem

        dim a(10,20),b(10,20),c(10,20)

        rem  initialization of the arrays a() and b()
        for y=1 to 10:for x=1 to 20
           a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
        next x:next y

        matadd(a(),b(),c())

        print "Result:"
        for x=1 to 20
           for y=10 to 1 step -1
              print c(y,x)," ";
           next y
           print
        next x

        sub matadd(m1(),m2(),r())

           rem  This sub will add the matrices m1() and m2()
           rem  elementwise and store the result within r()
           rem  This is not very useful but easy to implement.
           rem  However, this sub excels in checking its arguments
           rem  with arraydim() and arraysize()

           local x:local y

           if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
              error "Need two dimensional arrays as input"
           endif

           y=arraysize(m1(),1):x=arraysize(m1(),2)
           if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
              error "The two matrices cannot be added elementwise"
           endif

           if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
              error "The result cannot be stored in the third argument"
           endif

           local xx:local yy
           for xx=1 to x
              for yy=1 to y
                 r(yy,xx)=m1(yy,xx)+m2(yy,xx)
              next yy
           next xx

         end sub

        See also

        arraydim and dim.

        ------------------------------------------------------------------------
-------

        Name

        asc() ? accepts a string and returns the position of its first character
 within
        the ascii charset

        Synopsis

        a=asc(char$)

        Description

        The asc-function accepts a string, takes its first character and looks i
t up
        within the ascii-charset; this position will be returned. The asc-functi
on is
        the opposite of the chr$-function. There are valid uses for asc, however
,
        comparing strings (i.e. to bring them into alphabetical sequence) is not
 among
        them; in such many cases you might consider to compare strings directly 
with <,
        = and > (rather than converting a string to a number and comparing this
        number).

        Example

        input "Please enter a letter between 'a' and 'y': " a$
        if (a$<"a" or a$>"y") print a$," is not in the proper range":end
        print "The letter after ",a$," is ",chr$(asc(a$)+1)

        See also

        chr$

        ------------------------------------------------------------------------
-------

        Name

        asin() ? returns the arcus sine of its numeric argument

        Synopsis

        angle=asin(x)

        Description

        acos is the arcus sine-function, i.e. the inverse of the sin-function. O
r, more
        elaborate: It Returns the angle (in radians, not degrees !), which, fed 
to the
        sine-function will produce the argument passed to the asin-function.

        Example

        print asin(0.5),asin(sin(pi))

        This will print 0.523599 -2.06823e-13 which is ? and almost 0 respective
ly.

        See also

        sin, acos

        ------------------------------------------------------------------------
-------

        Name

        at() ? can be used in the print-command to place the output at a specifi
ed
        position

        Synopsis

        clear screen
        ?
        print at(a,b)
        print @(a,b)

        Description

        The at-clause takes two numeric arguments (e.g. at(2,3)) and can be inse
rted
        after the print-keyword. at() can be used only if clear screen has been
        executed at least once within the program (otherwise you will get an err
or).

        The two numeric arguments of the at-function may range from 0 to the wid
th of
        your terminal minus 1, and from 0 to the height of your terminal minus 1
; if
        any argument exceeds these values, it will be truncated accordingly. How
ever,
        yabasic has no influence on the size of your terminal (80x25 is a common
, but
        not mandatory), the size of your terminal and the maximum values accepta
ble
        within the at-clause may vary. To get the size of your terminal you may 
use the
        peek-function: peek("screenwidth") returns the width of your terminal an
d peek
        ("screenheight") its height.

        Example

        clear screen
        maxx=peek("screenwidth")-1:maxy=peek("screenheight")-1
        for x=0 to maxx
          print at(x,maxy*(0.5+sin(2*pi*x/maxx)/2)) "*"
        next x

        This example plots a full period of the sine-function across the screen.

        See also

        print, clear screen, color

        ------------------------------------------------------------------------
-------

        Name

        atan() ? returns the arctangent of its numeric argument

        Synopsis

        angle=atan(a,b)
        angle=atan(a)

        Description

        atan is the arctangent-function, i.e. the inverse of the tan-function. O
r, more
        elaborate: It Returns the angle (in radians, not degrees !), which, fed 
to the
        tan-function will produce the argument passed to the atan-function.

        The atan-function has a second form, which accepts two arguments: atan(a
,b)
        which is (mostly) equivalent to atan(a/b) except for the fact, that the
        two-argument-form returns an angle in the range -? to ?, whereas the
        one-argument-form returns an angle in the range -?/2 to ?/2. To understa
nd this
        you have to be good at math.

        Example

        print atan(1),atan(tan(pi)),atan(-0,-1),atan(-0,1)

        This will print 0.463648 2.06823e-13 -3.14159 3.14159 which is ?/4, almo
st 0,
        -? and ? respectively.

        See also

        tan, sin

        B

        backcolor ? change color for background of graphic window
        backcolour ? see backcolor
        beep ? ring the bell within your computer; a synonym for bell
        bell ? ring the bell within your computer (just as beep)
        bin$() ? converts a number into a sequence of binary digits
        bind() ? Binds a yabasic-program and the yabasic-interpreter together in
to a
            standalone program.
        box ? draw a rectangle. A synonym for rectangle
        break ? breaks out of one or more loops or switch statements

        Name

        color ? change color for background of graphic window

        Synopsis

        backcolour red,green,blue
        backcolour "red,green,blue"

        Description

        Change the color, that becomes visible, if any portion of the window is 
erased,
        e.g. after clear window or clear line. Note however, that parts of the w
indow,
        that display the old background color will not change.

        As with the color-command, the new background color can either be specif
ied as
        a triple of three numbers or as a single string, that contains those thr
ee
        numbers separated by commas.

        Example

        open window 255,255
        for x=10 to 235 step 10:for y=10 to 235 step 10
                backcolour x,y,0
                clear window
                sleep 1
        next y:next x

        This changes the background colour of the graphic window repeatedly and 
clears
        it every time, so that it is filled with the new background colour.

        See also

        open window, color, line, rectangle, triangle, circle

        ------------------------------------------------------------------------
-------

        Name

        backcolour ? see backcolor

        Synopsis

        backcolour red,green,blue
        backcolour "red,green,blue"

        See also

        color

        ------------------------------------------------------------------------
-------

        Name

        beep ? ring the bell within your computer; a synonym for bell

        Synopsis

        beep

        Description

        The bell-command rings the bell within your computer once. This command 
is not
        a sound-interface, so you can neither vary the length or the height of t
he
        sound (technically, it just prints \a). bell is exactly the same as beep
.

        Example

        beep:print "This is a problem ..."

        See also

        beep

        ------------------------------------------------------------------------
-------

        Name

        bell ? ring the bell within your computer (just as beep)

        Synopsis

        bell

        Description

        The beep-command rings the bell within your computer once. beep is a syn
onym
        for bell.

        Example

        print "This is a problem ...":beep

        See also

        bell

        ------------------------------------------------------------------------
-------

        Name

        bin$() ? converts a number into a sequence of binary digits

        Synopsis

        hexadecimal$=bin$(decimal)

        Description

        The bin$-function takes a single numeric argument an converts it into a 
string
        of binary digits (i.e. zeroes and ones). If you pass a negative number t
o bin$,
        the resulting string will be preceded by a '-'.

        If you want to convert the other way around (i.e. from binary to decimal
) you
        may use the dec-function.

        Example

        for a=1 to 100
          print bin$(a)
        next a

        This example prints the binary representation of all digits between 1 an
d 100.

        See also

        hex$, dec

        ------------------------------------------------------------------------
-------

        Name

        bind() ? Binds a yabasic-program and the yabasic-interpreter together in
to a
        standalone program.

        Synopsis

        bind("foo.exe")

        Description

        The bind-command combines your own yabasic-program (plus all the librari
es it
        does import) and the interpreter by copying them into a new file, whose 
name is
        passed as an argument. This new program may then be executed on any comp
uter,
        even if it does not have yabasic installed.

        Please see the section about creating a standalone-program for details.

        Example

        if (!peek("isbound")) then
          bind "foo"
          print "Successfully created the standalone executable 'foo' !"
          exit
        endif

        print "Hello World !"

        This example creates a standalone program foo from itself.

        See also

        The section about creating a standalone-program, the peek-function and t
he
        command line options.

        ------------------------------------------------------------------------
-------

        Name

        box ? draw a rectangle. A synonym for rectangle

        Synopsis

        See the rectangle-command.

        Description

        The box-command does exactly the same as the rectangle-command; it is ju
st a
        synonym. Therefore you should refer to the entry for the rectangle-comma
nd for
        further information.

        ------------------------------------------------------------------------
-------

        Name

        break ? breaks out of one or more loops or switch statements

        Synopsis

        break

        break 2

        Description

        break transfers control immediately outside the enclosing loop or switch
        statement. This is the preferred way of leaving a such a statement (rath
er than
        goto, which is still possible in most cases). An optional digit allows o
ne to
        break out of multiple levels, e.g. to leave a loop from within a switch
        statement. Please note, that only a literal (e.g. 2) is allowed at this
        location.

        Example

        for a=1 to 10
          break
          print "Hi"
        next a

        while(1)
          break
          print "Hi"
        wend

        repeat
          break
          print "Hi"
        until(0)

        switch 1
        case 1:break
        case 2:case 3:print "Hi"
        end switch

        This example prints nothing at all, because each of the loops (and the
        switch-statement) does an immediate break (before it could print any "Hi
").

        See also

        for, while, repeat and switch.

        C

        case ? mark the different cases within a switch-statement
        ceil() ? compute the ceiling for its (float) argument.
        chomp$() ? Remove a single trailing newline from its string-argument; if
 the
            string does not end in a newline, the string is returned unchanged.
        chr$() ? accepts a number and returns the character at this position wit
hin the
            ascii charset
        circle ? draws a circle in the graphic-window
        clear ? Erase circles, rectangles or triangles
        clear screen ? erases the text window
        clear window ? clear the graphic window and begin a new page, if printin
g is
            under way
        close ? close a file, which has been opened before
        close curve ? close a curve, that has been drawn by the line-command
        close printer ? stops printing of graphics
        close window ? close the graphics-window
        color ? change color for any subsequent drawing-command
        colour ? see color
        compile ? compile a string with yabasic-code on the fly
        continue ? start the next iteration of a for-, do-, repeat- or while-loo
p
        cos() ? return the cosine of its single argument

        Name

        case ? mark the different cases within a switch-statement

        Synopsis

        switch a
          case 1
          case 2
          ?
        end switch

        ?

        switch a$
          case "a"
          case "b"
          ?
        end switch

        Description

        Please see the switch-statement.

        Example

        input a
        switch(a)
          case 1:print "one":break
          case 2:print "two":break
          default:print "more"
        end switch

        Depending on your input (a number is expected) this code will print one 
or two
        or otherwise more.

        See also

        switch

        ------------------------------------------------------------------------
-------

        Name

        ceil() ? compute the ceiling for its (float) argument.

        Synopsis

        print ceil(x)

        Description

        The ceil-function returns the smallest integer number, that is larger or
 equal
        than its argument.

        Example

        print ceil(1.5),floor(1.5)
        print ceil(2),floor(2)

        Comparing functions ceil and floor, gives a first line of output (1 2), 
showing
        that ceil is less or equal than floor; but as the second line of output 
(2 2)
        shows, the two functions give equal results for integer arguments.

        See also

        floor, int, frac

        ------------------------------------------------------------------------
-------

        Name

        chomp$() ? Remove a single trailing newline from its string-argument; if
 the
        string does not end in a newline, the string is returned unchanged.

        Synopsis

        print chomp$("Hallo !\n")

        Description

        The chomp$-function checks, if its string-argument ends in a newline and
        removes it eventually; for this purpose chomp$ can replace an if-stateme
nt.
        This can be especially useful, when you deal with input from external so
urces
        like system$.

        You may apply chomp$ freely, as it only acts, if there is a newline to r
emove;
        note however, that user-input, that comes from the normal input-statemen
t, does
        not need such a treatment, because it already comes without a newline.

        Example

        The following yabasic-program uses the unix-command whoami to get the us
ername
        of the current user in order to greet him personally. This is done twice
: First
        with the chomp$-function and then again with with an equivalent if-state
ment:

        print "Hello " + chomp$(system$("whoami")) + " !"

        user$ = system$("whoami")
        if (right$(user$,1)="\n") user$=left$(user$,len(user$)-1)
        print "Hello again " + user$ + " !"

        See also

        system$

        ------------------------------------------------------------------------
-------

        Name

        chr$() ? accepts a number and returns the character at this position wit
hin the
        ascii charset

        Synopsis

        character$=chr$(ascii)

        Description

        The chr$-function is the opposite of the asc-function. It looks up and r
eturns
        the character at the given position within the ascii-charset. It's typic
al use
        is to construct nonprintable characters which do not occur on your keybo
ard.

        Nevertheless you won't use chr$ as often as you might think, because the
 most
        important nonprintable characters can be constructed using escape-sequen
ces
        using the \-character (e.g. you might use \n instead of chr$(10) whereve
r you
        want to use the newline-character).

        Example

        print "a",chr$(10),"b"

        This will print the letters 'a' and 'b' in different lines because of th
e
        intervening newline-character, which is returned by chr$(10).

        See also

        asc

        ------------------------------------------------------------------------
-------

        Name

        circle ? draws a circle in the graphic-window

        Synopsis

        circle x,y,r
        clear circle x,y,r
        fill circle x,y,r
        clear fill circle x,y,r

        Description

        The circle-command accepts three parameters: The x- and y-coordinates of
 the
        center and the radius of the circle.

        Some more observations related with the circle-command:

          * The graphic-window must have been opened already.

          * The circle may well extend over the boundaries of the window.

          * If you have issued open printer before, the circle will finally appe
ar in
            the printed hard copy of the window.

          * fill circle will draw a filled (with black ink) circle.

          * clear circle will erase (or clear) the outline of the circle.

          * clear fill circle or fill clear circle will erase the full area of t
he
            circle.

        Example

        open window 200,200

        for n=1 to 2000
          x=ran(200)
          y=ran(200)
          fill circle x,y,10
          clear fill circle x,y,8
        next n

        This code will open a window and draw 2000 overlapping circles within. E
ach
        circle is drawn in two steps: First it is filled with black ink (fill ci
rcle
        x,y,10), then most of this circle is erased again (clear fill circle x,y
,8). As
        a result each circle is drawn with an opaque white interior and a 2-pixe
l
        outline (2-pixel, because the radii differ by two).

        See also

        open window, open printer, line, rectangle, triangle

        ------------------------------------------------------------------------
-------

        Name

        clear ? Erase circles, rectangles or triangles

        Synopsis

        clear rectangle 10,10,90,90
        clear fill circle 50,50,20
        clear triangle 10,10,20,20,50,30

        Description

        May be used within the circle, rectangle or triangle command and causes 
these
        shapes to be erased (i.e. be drawn in the colour of the background).

        fill can be used in conjunction with and wherever the fill-clause may ap
pear.
        Used alone, clear will erase the outline (not the interior) of the shape
        (circle, rectangle or triangle); together with fill the whole shape (inc
luding
        its interior) is erased.

        Example

        open window 200,200
        fill circle 100,100,50
        clear fill rectangle 10,10,90,90

        This opens a window and draws a pacman-like figure.

        See also

        clear, circle, rectangle, triangle

        ------------------------------------------------------------------------
-------

        Name

        clear screen ? erases the text window

        Synopsis

        clear screen

        Description

        clear screen erases the text window (the window where the output of prin
t
        appears).

        It must be issued at least once, before some advanced screen-commands (e
.g.
        print at or inkey$) may be called; this requirement is due to some limit
ations
        of the curses-library, which is used by yabasic under Unix for some comm
ands.

        Example

        clear screen
        print "Please press a key : ";
        a$=inkey$
        print a$

        The clear screen command is essential here; if it would be omitted, yaba
sic
        would issue an error ("need to call 'clear screen' first") while trying 
to
        execute the inkey$-function.

        See also

        inkey$

        ------------------------------------------------------------------------
-------

        Name

        clear window ? clear the graphic window and begin a new page, if printin
g is
        under way

        Synopsis

        clear window

        Description

        clear window clears the graphic window. If you have started printing the
        graphic via open printer, the clear window-command starts a new page as 
well.

        Example

        open window 200,200
        open printer "t.ps"

        for a=1 to 10
        if (a>1) clear window
        text 100,100,"Hallo "+str$(a)
        next a

        close printer
        close window

        This example prints 10 pages, with the text "Hello 1", "Hello 2", ? and 
so on.
        The clear screen-command clears the graphics window and starts a new pag
e.

        See also

        open window, open printer

        ------------------------------------------------------------------------
-------

        Name

        close ? close a file, which has been opened before

        Synopsis

        close filenum
        close # filenum

        Description

        The close-command closes an open file. You should issue this command as 
soon as
        you are done with reading from or writing to a file.

        Example

        open "my.data" for reading as 1
        input #1 a
        print a
        close 1

        This program opens the file "my.data", reads a number from it, prints th
is
        number and closes the file again.

        See also

        open

        ------------------------------------------------------------------------
-------

        Name

        close curve ? close a curve, that has been drawn by the line-command

        Synopsis

        new curve
        line to x1,y1
        ?
        close curve

        Description

        The close curve-command closes a sequence of lines, that has been drawn 
by
        repeated line to-commands.

        Example

        open window 200,200
        new curve
        line to 100,50
        line to 150,150
        line to 50,150
        close curve

        This example draws a triangle: The three line to-commands draw two lines
; the
        final line is however not drawn explicitly, but drawn by the close
        curve-command.

        See also

        line, new curve

        ------------------------------------------------------------------------
-------

        Name

        close printer ? stops printing of graphics

        Synopsis

        close printer

        Description

        The close printer-command ends the printing graphics. Between open print
er and
        close printer everything you draw (e.g. circles, lines ?) is sent to you
r
        printer. close printer puts an end to printing and will make your printe
r eject
        the page.

        Example

        open window 200,200
        open printer
        circle 100,100,50
        close printer
        close window

        As soon as close printer is executed, your printer will eject a page wit
h a
        circle on it.

        See also

        open printer

        ------------------------------------------------------------------------
-------

        Name

        close window ? close the graphics-window

        Synopsis

        close window

        Description

        The close window-command closes the graphics-window, i.e. it makes it di
sappear
        from your screen. It includes an implicit close printer, if a printer ha
s been
        opened previously.

        Example

        open window 200,200
        circle 100,100,50
        close window

        This example will open a window, draw a circle and close the window agai
n; all
        this without any pause or delay, so the window will be closed before you
 may
        regard the circle..

        See also

        open window

        ------------------------------------------------------------------------
-------

        Name

        color ? change color for any subsequent drawing-command

        Synopsis

        colour red,green,blue
        colour "red,green,blue"

        Description

        Change the color, in which lines, dots, circles, rectangles or triangles
 are
        drawn. The color-command accepts three numbers in the range 0 ? 255 (as 
in the
        first line of the synopsis above). Those numbers specify the intensity f
or the
        primary colors red, green and blue respectively. As an example 255,0,0 i
s red
        and 255,255,0 is yellow.

        Alternatively you may specify the color with a single string (as in the 
second
        line of the synopsis above); this string should contain three numbers,
        separated by commas. As an example "255,0,255" would be violet. Using th
is
        variant of the colour-command, you may use symbolic names for colours:

        open window 100,100
        yellow$="255,255,0"
        color yellow$
        text 50,50,"Hallo"

        , which reads much clearer.

        Example

        open window 255,255
        for x=10 to 235 step 10:for y=10 to 235 step 10
                colour x,y,0
                fill rectangle x,y,x+10,y+10
        next y:next x

        This fills the window with colored rectangles. However, none of the used
        colours contains any shade of blue, because the color-command has always
 0 as a
        third argument.

        See also

        open window, backcolor, line, rectangle, triangle, circle

        ------------------------------------------------------------------------
-------

        Name

        colour ? see color

        Synopsis

        colour red,green,blue
        colour "red,green,blue"

        See also

        color

        ------------------------------------------------------------------------
-------

        Name

        compile ? compile a string with yabasic-code on the fly

        Synopsis

        compile(code$)

        Description

        This is an advanced command (closely related with the execute-command). 
It
        allows you to compile a string of yabasic-code (which is the only argume
nt).
        Afterwards the compiled code is a normal part of your program.

        Note, that there is no way to remove the compiled code.

        Example

        compile("sub mysub(a):print a:end sub")
        mysub(2)

        This example creates a function named mysub, which simply prints its sin
gle
        argument.

        See also

        execute

        ------------------------------------------------------------------------
-------

        Name

        continue ? start the next iteration of a for-, do-, repeat- or while-loo
p

        Synopsis

        continue

        Description

        You may use continue within any loop to start the next iteration immedia
tely.
        Depending on the type of the loop, the loop-condition will or will not b
e
        checked. Especially: for- and while-loops will evaluate their respective
        conditions, do- and repeat-loops will not.

        Remark: Another way to change the flow of execution within a loop, is th
e
        break-command.

        Example

        for a=1 to 100
          if mod(a,2)=0 continue
          print a
        next a

        This example will print all odd numbers between 1 and 100.

        See also

        for, do, repeat, while, break

        ------------------------------------------------------------------------
-------

        Name

        cos() ? return the cosine of its single argument

        Synopsis

        x=cos(angle)

        Description

        The cos-function expects an angle (in radians) and returns its cosine.

        Example

        print cos(pi)

        This example will print -1.

        See also

        acos, sin

        D

        data ? introduces a list of data-items
        date$ ? returns a string with various components of the current date
        dec() ? convert a base 2 or base 16 number into decimal form
        default ? mark the default-branch within a switch-statement
        dim ? create an array prior to its first use
        do ? start a (conditionless) do-loop
        doc ? special comment, which might be retrieved by the program itself
        docu$ ? special array, containing the contents of all docu-statement wit
hin the
            program
        dot ? draw a dot in the graphic-window

        Name

        data ? introduces a list of data-items

        Synopsis

        data 9,"world"
        ?
        read b,a$

        Description

        The data-keyword introduces a list of comma-separated list of strings or
        numbers, which may be retrieved with the read-command.

        The data-command itself does nothing; it just stores data. A single
        data-command may precede an arbitrarily long list of values, in which st
rings
        or numbers may be mixed at will.

        yabasic internally uses a data-pointer to keep track of the current loca
tion
        within the data-list; this pointer may be reset with the restore-command
.

        Example

        do
          restore
          for a=1 to 4
            read num$,num
            print num$,"=",num
          next a
        loop
        data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14

        This example just prints a series of lines eleven=11 up to fourteen=14 a
nd so
        on without end.

        The restore-command ensures that the list of data-items is read from the
 start
        with every iteration.

        See also

        read, restore

        ------------------------------------------------------------------------
-------

        Name

        date$ ? returns a string with various components of the current date

        Synopsis

        a$=date$

        Description

        The date$-function (which must be called without parentheses; i.e. date$
()
        would be an error) returns a string containing various components of a d
ate; an
        example would be 4-05-27-2004-Thu-May. This string consists of various f
ields
        separated by hyphens ("-"):

          * The day within the week as a number in the range 0 (=Sunday) to 6 (=
            Saturday) (in the example above: 4, i.e. Thursday).

          * The month as a number in the range 1 (=January) to 12 (=December) (i
n the
            example: 5 which stands for May).

          * The day within the month as a number in the range 1 to 31 (in the ex
ample:
            27).

          * The full, 4-digit year (in the example: 2004, which reminds me that 
I
            should adjust the clock within my computer ?).

          * The abbreviated name of the day within the week (Mon to Sun).

          * The abbreviated name of the month (Jan to Dec).

        Therefore the whole example above (4-05-27-2004-Thu-May) would read: day
 4 in
        the week (counting from 0), May 27 in the year 2004, which is a Thursday
 in
        May.

        Note, that all fields within the string returned by date$ have a fixed w
ith
        (numbers are padded with zeroes); therefore it is easy to extract the va
rious
        fields of a date format with mid$.

        Example

        rem   Two ways to print the same ...

        print mid$(date$,3,10)

        dim fields$(6)
        a=split(date$,fields$(),"-")
        print fields$(2),"-",fields$(3),"-",fields$(4)

        This example shows two different techniques to extract components from t
he
        value returned by date$. The mid$-function is the preferred way, but you
 could
        just as well split the return-value of date$ at every "-" and store the 
result
        within an array of strings.

        See also

        time$

        ------------------------------------------------------------------------
-------

        Name

        dec() ? convert a base 2 or base 16 number into decimal form

        Synopsis

        a=dec(number$)
        a=dec(number$,base)

        Description

        The dec-function takes the string-representation of a base-2 or base-16 
(which
        is the default) number and converts it into a decimal number. The option
al
        second argument (base) might be used to specify a base other than 16. Ho
wever,
        currently only base 2 or base 16 are supported. Please note, that for ba
se 16
        you may write literals in the usual way, by preceding them with 0x, e.g.
 like

        print 0xff

        ; this may save you from applying the dec altogether.

        Example

        input "Please enter a binary number: " a$
        print a$," is ",dec(a$)

        See also

        bin$, hex$

        ------------------------------------------------------------------------
-------

        Name

        default ? mark the default-branch within a switch-statement

        Synopsis

        switch a+3
        case 1
          ?
        case 2
          ?
        default
          ?
        end switch

        Description

        The default-clause is an optional part of the switch-statement (see ther
e for
        more information). It introduces a series of statements, that should be
        executed, if none of the cases matches, that have been specified before 
(each
        with its own case-clause).

        So default specifies a default to be executed, if none of the explicitly
 named
        cases matches; hence its name.

        Example

        print "Please enter a number between 0 and 6,"
        print "specifying a day in the week."
        input d
        switch d
        case 0:print "Monday":break
        case 1:print "Tuesday":break
        case 2:print "Wednesday":break
        case 3:print "Thursday":break
        case 4:print "Friday":break
        case 5:print "Saturday":break
        case 6:print "Sunday":break
        default:print "Hey you entered something invalid !"
        end switch

        This program translates a number between 0 and 6 into the name of a week
day;
        the default-case is used to detect (and complain about) invalid input.

        See also

        sub, case

        ------------------------------------------------------------------------
-------

        Name

        dim ? create an array prior to its first use

        Synopsis

        dim array(x,y)
        dim array$(x,y)

        Description

        The dim-command prepares one or more arrays (of either strings or number
s) for
        later use. This command can also be used to enlarges an existing array.

        When an array is created with the dim-statement, memory is allocated and
 all
        elements are initialized with either 0 (for numerical arrays) or "" (for
 string
        arrays).

        If the array already existed, and the dim-statement specifies a larger s
ize
        than the current size, the array is enlarged and any old content is pres
erved.

        Note, that dim cannot be used to shrink an array: If you specify a size,
 that
        is smaller than the current size, the dim-command does nothing.

        Finally: To create an array, that is only known within a single subrouti
ne, you
        should use the command local, which creates local variables as well as l
ocal
        arrays.

        Example

        dim a(5,5)
        for x=1 to 5:for y=1 to 5
          a(x,y)=int(ran(100))
        next y:next x
        printmatrix(a())
        dim a(7,7)
        printmatrix(a())

        sub printmatrix(ar())
          local x,y,p,q
          x=arraysize(ar(),1)
          y=arraysize(ar(),2)
          for q=1 to y
            for p=1 to y
              print ar(p,q),"\t";
            next p
            print
          next q
        end sub

        This example creates a 2-dimensional array (i.e. a matrix) with the
        dim-statement and fills it with random numbers. The second dim-statement
        enlarges the array, all new elements are filled with 0.

        The subroutine printmatrix just does, what its name says.

        See also

        arraysize, arraydim, local

        ------------------------------------------------------------------------
-------

        Name

        do ? start a (conditionless) do-loop

        Synopsis

        do
        ?
        loop

        Description

        Starts a loop, which is terminated by loop; everything between do and lo
op will
        be repeated forever. This loop has no condition, so it is an infinite lo
op;
        note however, that a break- or goto-statement might be used to leave thi
s loop
        anytime.

        Example

        do
          a=a+1
          print a
          if (a>100) break
        loop

        This example prints the numbers between 1 and 101. The break-statement i
s used
        to leave the loop.

        See also

        loop, repeat, while, break

        ------------------------------------------------------------------------
-------

        Name

        doc ? special comment, which might be retrieved by the program itself

        Synopsis

        doc   This is a comment
        docu  This is another comment

        Description

        Introduces a comment, which spans up to the end of the line. But other t
han the
        rem-comment, any docu-comment is collected within the special docu$-arra
y and
        might be retrieved later on. Moreover you might invoke yabasic -docu foo
.yab on
        the command line to retrieve the embedded documentation within the progr
am
        foo.yab.

        Instead of doc you may just as well write docu or even documentation.

        Example

        rem   Hi, this has been written by me
        rem
        doc   This program asks for a number and
        doc   prints this number multiplied with 2
        rem
        rem   Print out rhe above message
        for a=1 to arraysize(docu$()):print docu$(a):next a

        rem   Read and print the number
        input "Please input a number: " x
        print x*2

        This program uses the comments within its code to print out a help messa
ge for
        the user.

        The contents of the doc-lines are retrieved from the docu$-array; if you
 do not
        want a comment to be collected within this array, use the rem-statement
        instead.

        See also

        docu$, rem

        ------------------------------------------------------------------------
-------

        Name

        docu$ ? special array, containing the contents of all docu-statement wit
hin the
        program

        Synopsis

        a$=docu$(1)

        Description

        Before your program is executed, yabasic collects the content of all the
        doc-statements within your program within this 1-dimensional array (well
 only
        those within the main-program, libraries are skipped).

        You may use the arraysize function to find out, how many lines it contai
ns.

        Example

        docu
        docu  This program reads two numbers
        docu  and adds them.
        docu

        rem retrieve and print the embedded documentation
        for a=1 to arraysize(docu$(),1)
          print docu$(a)
        next a

        input "First number: " b
        input "Second number: " c

        print "The sum of ",b," and ",c," is ",b+c

        This program uses the embedded documentation to issue a usage-message.

        See also

        arraydim, rem

        ------------------------------------------------------------------------
-------

        Name

        dot ? draw a dot in the graphic-window

        Synopsis

        dot x,y
        clear dot x,y

        Description

        Draws a dot at the specified coordinates within your graphic-window. If
        printing is in effect, the dot appears on your printout too.

        Use the functions peek("winheight") or peek("winwidth") to get the size 
of your
        window and hence the boundaries of the coordinates specified for the
        dot-command.

        Example

        open window 200,200
        circle 100,100,100
        do
          x=ran(200):y=ran(200)
          dot x,y
          total=total+1
          if (sqrt((x-100)^2+(y-100)^2)<100) in=in+1
          print 4*in/total
        loop

        This program uses a well known algorithm to compute ?.

        See also

        line, open window

        E

        else ? mark an alternative within an if-statement
        elsif ? starts an alternate condition within an if-statement
        end ? terminate your program
        endif ? ends an if-statement
        end sub ? ends a subroutine definition
        eof ? check, if an open file contains data
        eor() ? compute the bitwise exclusive or of its two arguments
        error ? raise an error and terminate your program
        euler ? another name for the constant 2.71828182864
        execute$() ? execute a user defined subroutine, which must return a stri
ng
        execute() ? execute a user defined subroutine, which must return a numbe
r
        exit ? terminate your program
        exp() ? compute the exponential function of its single argument
        export ? mark a function as globally visible

        Name

        else ? mark an alternative within an if-statement

        Synopsis

        if (?) then
          ?
        else
          ?
        endif

        Description

        The else-statement introduces the alternate branch of an if-statement. I
.e. it
        starts the sequence of statements, which is executed, if the condition o
f the
        if-statement is not true.

        Example

        input "Please enter a number: " a
        if (mod(a,2)=1) then
          print a," is odd."
        else
          print a," is even."
        endif

        This program detects, if the number you have entered is even or odd.

        See also

        if

        ------------------------------------------------------------------------
-------

        Name

        elsif ? starts an alternate condition within an if-statement

        Synopsis

        if (?) then
          ?
        elseif (?)
          ?
        elsif (?) then
          ?
        else
          ?
        endif

        Description

        The elsif-statement is used to select a single alternative among a serie
s of
        choices.

        With each elsif-statement you may specify a condition, which is tested, 
if the
        main condition (specified with the if-statement) has failed. Note that e
lsif
        might be just as well written as elseif.

        Within the example below, two variables a and b are tested against a ran
ge of
        values. The variable a is tested with the elsif-statement. The very same
 tests
        are performed for the variable b too; but here an involved series of
        if-else-statements is employed, making the tests much more obscure.

        Example

        input "Please enter a number: " a
        if (a<0) then
          print "less than 0"
        elseif (a<=10) then
          print "between 0 and 10"
        elsif (a<=20)
          print "between 11 and 20"
        else
          print "over 20"
        endif

        input "Please enter another number: " b
        if (b<0) then
          print "less than 0"
        else
          if (b<=10) then
            print "between 0 and 10"
          else
            if (b<=20) then
              print "between 11 and 20"
            else
              print "over 20"
            endif
          endif
        endif

        Note, that the very same tests are performed for the variables a and b, 
but can
        be stated much more clearly with the elsif-statement.

        Note, that elsif might be written as elseif too, and that the keyword th
en is
        optional.

        See also

        if, else

        ------------------------------------------------------------------------
-------

        Name

        end ? terminate your program

        Synopsis

        end

        Description

        Terminate your program. Much (but not exactly) like the exit command.

        Note, that end may not end your program immediately; if you have opened 
a
        window or called clear screen, yabasic assumes, that your user wants to 
study
        the output of your program after it has ended; therefore it issues the l
ine
        ---Program done, press RETURN--- and waits for a key to be pressed. If y
ou do
        not like this behaviour, consider using exit.

        Example

        print "Do you want to continue ?"
        input "Please answer y(es) or n(o): " a$
        if (lower$(left$(a$,1))="n") then
          print "bye"
          end
        fi

        See also

        exit

        ------------------------------------------------------------------------
-------

        Name

        endif ? ends an if-statement

        Synopsis

        if (?) then
          ?
        endif

        Description

        The endif-statement closes (or ends) an if-statement.

        Note, that endif may be written in a variety of other ways: end if, end-
if or
        even fi.

        The endif-statement must be omitted, if the if-statement does not contai
n the
        keyword then (see the example below). Such an if-statement without endif
        extends only over a single line.

        Example

        input "A number please: " a
        if (a<10) then
          print "Your number is less than 10."
        endif

        REM  and now without endif

        input "A number please: " a
        if (a<10) print "Your number is less than 10."

        See also

        if

        ------------------------------------------------------------------------
-------

        Name

        end sub ? ends a subroutine definition

        Synopsis

        sub foo(?)
          ?
        end sub

        Description

        Marks the end of a subroutine-definition (which starts with the sub-keyw
ord).
        The whole concept of subroutines is explained within the entry for sub.

        Example

        print foo(3)

        sub foo(a)
          return a*2
        end sub

        This program prints out 6. The subroutine foo simply returns twice its
        argument.

        See also

        sub

        ------------------------------------------------------------------------
-------

        Name

        eof ? check, if an open file contains data

        Synopsis

        open 1,"foo.bar"
        if (eof(1)) then
           ?
        end if

        Description

        The eof-function checks, if there is still data left within an open file
. As an
        argument it expects the file-number as returned by (or used within) the
        open-function (or statement).

        Example

        a=open("foo.bar")
        while(not eof(a))
          input #a,a$
          print a$
        end while

        This example will print the contents of the file "foo.bar". The eof-func
tion
        will terminate the loop, if there is no more data left within the file.

        See also

        open

        ------------------------------------------------------------------------
-------

        Name

        eor() ? compute the bitwise exclusive or of its two arguments

        Synopsis

        print eor(a,b)

        Description

        The eor-function takes two arguments and computes their bitwise exclusiv
e or.
        See your favorite introductory text on informatics for an explanation of
 this
        function.

        The xor-function is the same as the eor function; both are synonymous; h
owever
        they have each their own description, so you may check out the entry of 
xor for
        a slightly different view.

        Example

        for a=0 to 3
          for b=0 to 3
            print fill$(bin$(a))," eor ",fill$(bin$(b))," = ",fill$(bin$(eor(a,b
)))
          next b
        next a

        sub fill$(a$)
          return right$("0"+a$,2)
        end sub

        This example prints a table, from which you may figure, how the eor-func
tion is
        computed.

        See also

        and, or

        ------------------------------------------------------------------------
-------

        Name

        error ? raise an error and terminate your program

        Synopsis

        error "Wrong, wrong, wrong !!"

        Description

        Produces the same kind or error messages, that yabasic itself produces (
e.g. in
        case of a syntax-error). The single argument is issued along with the cu
rrent
        line-number.

        Example

        input "Please enter a number between 1 and 10: " a
        if (a<1 or a>10) error "Oh no ..."

        This program is very harsh in checking the users input; instead of just 
asking
        again, the program terminates with an error, if the user enters somethin
g
        wrong.

        The error message would look like this:

        ---Error in t.yab, line 2: Oh no ...
        ---Error: Program stopped due to an error

        See also

        Well, there should be a corresponding called warning; unfortunately ther
 is
        none yet.

        ------------------------------------------------------------------------
-------

        Name

        euler ? another name for the constant 2.71828182864

        Synopsis

        foo=euler

        Description

        euler is the well known constant named after Leonard Euler; its value is
        2.71828182864. euler is not a function, so parens are not allowed (i.e. 
euler()
        will produce an error). Finally, you may not assign to euler; it wouldn'
t sense
        anyway, because it is a constant.

        Example

        print euler

        See also

        pi

        ------------------------------------------------------------------------
-------

        Name

        execute$() ? execute a user defined subroutine, which must return a stri
ng

        Synopsis

        print execute$("foo$","arg1","arg2")

        Description

        execute$ can be used to execute a user defined subroutine, whose name ma
y be
        specified as a string expression.

        This feature is the only way to execute a subroutine, whose name is not 
known
        by the time you write your program. This might happen, if you want to ex
ecute a
        subroutine, which is compiled (using the compile command) during the cou
rse of
        execution of your program.

        Note however, that the execute$-function is not the preferred method to 
execute
        a user defined subroutine; in almost all cases you should just execute a
        subroutine by writing down its name within your yabasic program (see the
        example).

        Example

        print execute$("foo$","Hello","world !")
        sub foo$(a$,b$)
          return a$+" "+b$
        end sub

        The example simply prints Hello world !, which is the return value of th
e user
        defined subroutine foo$. The same could be achieved by executing:

        print foo$(a$,b$)

        See also

        compile, execute

        ------------------------------------------------------------------------
-------

        Name

        execute() ? execute a user defined subroutine, which must return a numbe
r

        Synopsis

        print execute("bar","arg1","arg2")

        Description

        The execute-function is the counterpart of the execute$-function (please
 see
        there for some caveats). execute executes subroutines, which returns a n
umber.

        Example

        print execute("bar",2,3)
        sub bar(a,b)
          return a+b
        end sub

        See also

        compile, execute$

        ------------------------------------------------------------------------
-------

        Name

        exit ? terminate your program

        Synopsis

        exit
        exit 1

        Description

        Terminate your program and return any given value to the operating syste
m. exit
        is similar to end, but it will terminate your program immediately, no ma
tter
        what.

        Example

        print "Do you want to continue ?"
        input "Please answer y(es) or n(o): " a$
        if (lower$(left$(a$,1))="n") exit 1

        See also

        end

        ------------------------------------------------------------------------
-------

        Name

        exp() ? compute the exponential function of its single argument

        Synopsis

        foo=exp(bar)

        Description

        This function computes e to the power of its argument, where e is the we
ll
        known euler constant 2.71828182864.

        The exp-function is the inverse of the log-function.

        Example

        open window 100,100
        for x=0 to 100
           dot x,100-100*exp(x/100)/euler
        next x

        This program plots part of the exp-function, however the range is rather
 small,
        so that you may not recognize the function from this plot.

        See also

        log

        ------------------------------------------------------------------------
-------

        Name

        export ? mark a function as globally visible

        Synopsis

        export sub foo(bar)
        ?
        end sub

        Description

        The export-statement is used within libraries to mark a user defined sub
routine
        as visible outside the library wherein it is defined. Subroutines, which
 are
        not exported, must be qualified with the name of the library, e.g. foo.b
az
        (where foo is the name of the library and baz the name of the subroutine
);
        exported subroutines may be used without specifying the name of the libr
ary,
        e.g. bar.

        Therefore export may only be useful within libraries.

        Example

        The library foo.bar (which is listed below) defines two functions bar an
d baz,
        however only the function bar is exported and therefore visible even out
side
        the library; baz is not exported and may only be used within the library
        foo.yab:

        export sub bar()
          print "Hello"
        end sub

        sub baz()
          print "World"
        end sub

        Now within your main program cux.yab (which imports the library foo.yab)
; note
        that this program produces an error:

        import foo

        print "Calling subroutine foo.bar (okay) ..."
        foo.bar()
        print "done."

        print "Calling subroutine bar (okay) ..."
        bar()
        print "done."

        print "Calling subroutine foo.baz (okay) ..."
        foo.baz()
        print "done."

        print "Calling subroutine baz (NOT okay) ..."
        baz()
        print "done."

        The output when executing yabasic foo.yab is this:

        Calling subroutine foo.bar (okay) ...
        Hello
        done.
        Calling subroutine bar (okay) ...
        Hello
        done.
        Calling subroutine foo.baz (okay) ...
        World
        done.
        Calling subroutine baz (NOT okay) ...
        ---Error in main.yab, line 16: can't find subroutine 'baz'
        ---Dump: sub baz() called in main.yab,16
        ---Error: Program stopped due to an error

        As the error message above shows, the subroutine baz must be qualified w
ith the
        name of the library, if used outside the library, wherein it is defined 
(e.g.
        foo.baz. I.e. outside the library foo.yab you need to write foo.baz. baz
 alone
        would be an error.

        The subroutine bar (without adding the name of the library) however may 
(and
        probably should) be used in any program, which imports the library foo.y
ab.

        Note

        In some sense the set of exported subroutines constitutes the interface 
of a
        library.

        See also

        sub, import

        F

        false ? a constant with the value of 0
        fi ? another name for endif
        fill ? draw a filled circles, rectangles or triangles
        floor() ? compute the floor for its (float) argument.
        for ? starts a for-loop
        frac() ? return the fractional part of its numeric argument

        Name

        false ? a constant with the value of 0

        Synopsis

        okay=false

        Description

        The constant false can be assigned to variables which later appear in
        conditions (e.g. within an if-statement.

        false may also be written as FALSE or even FaLsE.

        Example

        input "Please enter a number between 1 and 10: " a
        if (check_input(a)) print "Okay"

        sub check_input(x)
          if (x>10 or x<1) return false
          return true
        end sub

        The subroutine check_input checks its argument and returns true or false
        according to the outcome of the check..

        See also

        true

        ------------------------------------------------------------------------
-------

        Name

        fi ? another name for endif

        Synopsis

        if (?)
        ?
        fi

        Description

        fi marks the end of an if-statement and is exactly equivalent to endif, 
please
        see there for further information.

        Example

        input "A number please: " a
        if (a<10) then
          print "Your number is less than 10."
        fi

        See also

        endif

        ------------------------------------------------------------------------
-------

        Name

        fill ? draw a filled circles, rectangles or triangles

        Synopsis

        fill rectangle 10,10,90,90
        fill circle 50,50,20
        fill triangle 10,20,20,10,20,20

        Description

        The keyword fill may be used within the circle, rectangle or triangle co
mmand
        and causes these shapes to be filled.

        fill can be used in conjunction with and wherever the clear-clause may a
ppear.
        Used alone, fill will fill the interior of the shape (circle, rectangle 
or
        triangle); together with clear the whole shape (including its interior) 
is
        erased.

        Example

        open window 200,200
        fill circle 100,100,50
        clear fill rectangle 10,10,90,90

        This opens a window and draws a pacman-like figure.

        See also

        clear, circle, rectangle, triangle

        ------------------------------------------------------------------------
-------

        Name

        floor() ? compute the floor for its (float) argument.

        Synopsis

        print floor(x)

        Description

        The floor-function returns the largest integer number, that is smaller o
r equal
        than its argument. For positive numbers x, floor(x) is the same as int(x
); for
        negaive numbers it can be different (see the example below).

        Example

        print int(-1.5),floor(-1.5)
        print int(-1),floor(-1)
        print int(1.5),floor(1.5)

        This example compares the functions int and floor, starting with -1 -2, 
then -1
        -1 and ending with 1 1, which shows the different behaviour of both func
tions.

        See also

        ceil, int, frac

        ------------------------------------------------------------------------
-------

        Name

        for ? starts a for-loop

        Synopsis

        for a=1 to 100 step 2
          ?
        next a

        Description

        The for-loop lets its numerical variable (a in the synopsis) assume all 
values
        within the given range. The optional step-clause may specify a value (de
fault:
        1) by which the variable will be incremented (or decremented, if step is
        negative).

        Any for-statement can be replaced by a set of ifs and gotos; as you may 
infer
        from the example below this is normally not feasible. However if you wan
t to
        know in detail how the for-statement works, you should study this exampl
e,
        which presents a for-statement and an exactly equivalent series of ifs a
nd
        gotos.

        Example

        for a=1 to 10 step 2:print a:next

        a=1
        label check
        if (a>10) goto done
          print a
          a=a+2
        goto check
        label done

        This example simply prints the numbers 1, 3, 5, 7 and 9. It does this tw
ice:
        First with a simple for-statement and then with ifs and gotos.

        See also

        step, next

        ------------------------------------------------------------------------
-------

        Name

        frac() ? return the fractional part of its numeric argument

        Synopsis

        x=frac(y)

        Description

        The frac-function takes its argument, removes all the digits to the left
 of the
        comma and just returns the digits right of the comma, i.e. the fractiona
l part.

        Refer to the example to learn how to rewrite frac by employing the int-f
unction
        (which is not suggested anyway).

        Example

        for a=1 to 10
          print frac(sqr(a))
          print sqr(a)-int(sqr(a))
        next a

        The example prints the fractional part of the square root of the numbers
        between 1 and 10. Each result is computed (and printed) twice: Once by
        employing the frac-function and once by employing the int-function.

        See also

        int, floor, ceil

        G

        getbit$() ? return a string representing the bit pattern of a rectangle 
within
            the graphic window
        getscreen$() ? returns a string representing a rectangular section of th
e text
            terminal
        glob() ? check if a string matches a simple pattern
        gosub ? continue execution at another point within your program (and ret
urn
            later)
        goto ? continue execution at another point within your program (and neve
r come
            back)

        Name

        getbit$() ? return a string representing the bit pattern of a rectangle 
within
        the graphic window

        Synopsis

        a$=getbit$(10,10,20,20)
        a$=getbit$(10,10 to 20,20)

        Description

        The function getbit returns a string, which contains the encoded bit-pat
tern of
        a rectangle within graphic window; the four arguments specify two opposi
te
        corners of the rectangle. The string returned might later be fed to the 
putbit
        -command.

        The getbit$-function might be used for simple animations (as in the exam
ple
        below).

        Example

        open window 40,40
        fill circle 20,20,18
        circle$=getbit$(0,0,40,40)
        close window

        open window 200,200
        for x=1 to 200
          putbit circle$,x,80
        next x

        This example features a circle moving from left to right over the window
.

        See also

        putbit

        ------------------------------------------------------------------------
-------

        Name

        getscreen$() ? returns a string representing a rectangular section of th
e text
        terminal

        Synopsis

        a$=getscreen$(2,2,20,20)

        Description

        The getscreen$ function returns a string representing the area of the sc
reen as
        specified by its four arguments (which specify two opposite corners). I.
e.
        everything you have printed within this rectangle will be encoded in the
 string
        returned (including any colour-information).

        Like most other commands dealing with advanced text output, getscreen$
        requires, that you have called clear screen before.

        Example

        clear screen

        for a=1 to 1000:
                print color("red") "1";
                print color("green") "2";
                print color("blue") "3";
        next a
        screen$=getscreen$(10,10,40,10)
        print at(10,10) " Please Press 'y' or 'n' ! "
        a$=inkey$
        putscreen screen$,10,10

        This program fills the screen with colored digits and afterwards asks th
e user
        for a choice ( Please press 'y' or 'n' ! ). Afterwards the area of the s
creen,
        which has been overwritten by the question will be restored with its pre
vious
        contents, whhch had been saved via getscreen$.

        See also

        putscreen$

        ------------------------------------------------------------------------
-------

        Name

        glob() ? check if a string matches a simple pattern

        Synopsis

        if (glob(string$,pattern$)) ?

        Description

        The glob-function takes two arguments, a string and a (glob-) pattern, a
nd
        checks if the string matches the pattern. However glob does not employ t
he
        powerful rules of regular expressions; rather it has only two special
        characters: * (which matches any number (even zero) of characters) and ?
 (which
        matches exactly a single character).

        Example

        for a=1 to 10
          read string$,pattern$
          if (glob(string$,pattern$)) then
            print string$," matches ",pattern$
          else
            print string$," does not match ",pattern$
          endif
        next a

        data "abc","a*"
        data "abc","a?"
        data "abc","a??"
        data "abc","*b*"
        data "abc","*"
        data "abc","???"
        data "abc","?"
        data "abc","*c"
        data "abc","A*"
        data "abc","????"

        This program checks the string abc against various patterns and prints t
he
        result. The output is:

        abc matches a*
        abc does not match a?
        abc matches a??
        abc matches *b*
        abc matches *
        abc matches ???
        abc does not match ?
        abc matches *c
        abc does not match A*
        abc does not match ????

        See also

        There are no related commands.

        ------------------------------------------------------------------------
-------

        Name

        gosub ? continue execution at another point within your program (and ret
urn
        later)

        Synopsis

        gosub foo

        ?

        label foo
        ?
        return

        Description

        gosub remembers the current position within your program and then passes
 the
        flow of execution to another point (which is normally marked with a labe
l).
        Later, when a return-statement is encountered, the execution is resumed 
at the
        previous location.

        gosub is the traditional command for calling code, which needs to be exe
cuted
        from various places within your program. However, with subroutines yabas
ic
        offers a much more flexible way to achieve this (and more). Therefore go
sub
        must to be considered obsolete.

        Example

        print "Do you want to exit ? "
        gosub ask
        if (r$="y") exit

        label ask
        input "Please answer yes or no, by typing 'y' or 'n': ",r$
        return

        See also

        return, goto, sub, label, on gosub

        ------------------------------------------------------------------------
-------

        Name

        goto ? continue execution at another point within your program (and neve
r come
        back)

        Synopsis

        goto foo

        ?

        label foo

        Description

        The goto-statement passes the flow of execution to another point within 
your
        program (which is normally marked with a label).

        goto is normally considered obsolete and harmful, however in yabasic it 
may be
        put to the good use of leaving loops (e.g. while or for) prematurely. No
te
        however, that subroutines may not be left with the goto-statement.

        Example

        print "Please press any key to continue."
        print "(program will continue by itself within 10 seconds)"
        for a=1 to 10
          if (inkey$(1)<>"") then goto done
        next a
        label done
        print "Hello World !"

        Here the goto-statement is used to leave the for-loop prematurely.

        See also

        gosub, on goto

        H

        hex$() ? convert a number into hexadecimal

        Name

        hex$() ? convert a number into hexadecimal

        Synopsis

        print hex$(foo)

        Description

        The hex$-function converts a number into a string with its hexadecimal
        representation. hex$ is the inverse of the dec-function.

        Example

        open 1,"foo"
        while(!eof(1))
          print right$("0"+hex$(peek(1)),2)," ";
          i=i+1
          if (mod(i,10)=0) print
        end while
        print

        This program reads the file foo and prints its output as a hex-dump usin
g the
        hex-function.

        See also

        decbin

        I

        if ? evaluate a condition and execute statements or not, depending on th
e
            result
        import ? import a library
        inkey$ ? wait, until a key is pressed
        input ? read input from the user (or from a file) and assign it to a var
iable
        instr() ? searches its second argument within the first; returns its pos
ition
            if found
        int() ? return the integer part of its single numeric argument

        Name

        if ? evaluate a condition and execute statements or not, depending on th
e
        result

        Synopsis

        if (?) then
          ?
        endif

        if (?) ?

        if (?) then
          ?
        else
          ?
        endif

        if (?) then
          ?
        elsif (?)
          ?
        elsif (?) then
          ?
        else
          ?
        endif

        Description

        The if-statement is used to evaluate a conditions and take actions accor
dingly.
        (As an aside, please note that there is no real difference between condi
tions
        and expressions.)

        There are two major forms of the if-statement:

          * The one-line-form without the keyword then:

            if (?) ?

            This form evaluates the condition and if the result is true executes
 all
            commands (separated by colons) upt to the end of the line. There is 
neither
            an endif keyword nor an else-branch.

          * The multi-line-form with the keyword then:

            if (?) then ? elsif (?) ? else ? endif

            (where elsif and else are optional, whereas endif is not.

            According to the requirements of your program, you may specify:

              + elsif(?), which specifies a condition, that will be evaluated on
ly if
                the condition(s) within if or any preceding elsif did not match.

              + else, which introduces a sequence of commands, that will be exec
uted,
                if none of the conditions above did match.

              + endif is required and ends the if-statement.

        Example

        input "Please enter a number between 1 and 4: " a
        if (a<=1 or a>=4) error "Wrong, wrong !"
        if (a=1) then
          print "one"
        elsif (a=2)
          print "two"
        elsif (a=3)
          print "three"
        else
          print "four"
        endif

        The input-number between 1 and 4 is simply echoed as text (one, two, ?).
 The
        example demonstrates both forms (short and long) of the if-statement (No
te
        however, that the same thing can be done, probably somewhat more elegant
, with
        the switch-statement).

        See also

        else, elsif, endif, conditions and expressions.

        ------------------------------------------------------------------------
-------

        Name

        import ? import a library

        Synopsis

        import foo

        Description

        The import-statement imports a library. It expects a single argument, wh
ich
        must be the name of a library (without the trailing .yab). This library 
will
        then be read and parsed and its subroutines (and variables) will be made
        available within the importing program. Most of the time this will be th
e main
        program, but libraries my also import and use other libraries.

        Libraries will first be searched in three locations in order:

          * The current directory, i.e. the directory from which you have invoke
d
            yabasic)

          * The directory, where your main program lives. This can be different 
from
            the first directory, if you specify a path for your main program, e.
g. like
            yabasic foo/bar.yab.

          * Finally, libraries are searched within a special directory, whose ex
act
            location depends on your system or options when invoking yabasic. Ty
pical
            values would be /usr/lib under Unix or C:\yabasic\lib under Windows.
            Invoking yabasic --help will show the correct directory. The locatio
n of
            this directory may be changed with the option --librarypath (see opt
ions).

        Example

        Lets say you have a yabasic-program foo.yab, which imports a library lib
.yab.
        foo.yab; this would read:

        import lib

        rem  This works
        lib.x(0)

        rem  This works too
        x(1)

        rem  And this
        lib.y(2)

        rem  But this not !
        y(3)

        Now the library lib.yab reads:

        rem  Make the subroutine x easily available outside this library
        export sub x(a)
          print a
          return
        end sub

        rem  sub y must be referenced by its full name
        rem  outside this library
        sub y(a)
          print a
          return
        end sub

        This program produces an error:

        0
        1
        2
        ---Error in foo.yab, line 13: can't find subroutine 'y'
        ---Dump: sub y() called in foo.yab,13
        ---Error: Program stopped due to an error

        As you may see from the error message, yabasic is unable to find the sub
routine
        y without specifying the name of the library (i.e. lib.y). The reason fo
r this
        is, that y, other than x, is not exported from the library lib.yab (usin
g the
        export-statement).

        See also

        export, sub

        ------------------------------------------------------------------------
-------

        Name

        inkey$ ? wait, until a key is pressed

        Synopsis

        clear screen
        foo$=inkey$
        inkey$
        foo$=inkey$(bar)
        inkey$(bar)

        Description

        The inkeys$-function waits, until the user presses a key on the keyboard
 or a
        button of his mouse, and returns this very key. An optional argument spe
cifies
        the number of seconds to wait; if omitted, inkey$ will wait indefinitely
.

        inkey$ may only be used, if clear screen has been called at least once.

        For normal keys, yabasic simply returns the key, e.g. a, 1 or !. For fun
ction
        keys you will get f1, f2 and so on. Other special keys will return these
        strings respectively: enter, backspace, del, esc, scrnup (for screen up)
,
        scrndown and tab. Modifier keys (e.g. ctrl, alt or shift) by themselves 
can not
        be detected (e.g. if you simultaneously press shift and 'a', inkey$ will
 return
        the letter 'A' instead of 'a' of course).

        If a graphical window has been opened (via open window) any mouseclick w
ithin
        this window will be returned by inkey$ too. The string returned (e.g.
        MB1d+0:0028,0061, MB2u+0:0028,0061 or MB1d+1:0028,0061) is constructed a
s
        follows:

          * Every string associated with a mouseclick will start with the fixed 
string
            MB

          * The next digit (1, 2 or 3) specifies the mousebutton pressed.

          * A single letter, d or u, specifies, if the mousebutton has been pres
sed or
            released: d stands for down, i.e. the mousebutton has been pressed; 
u means
            up, i.e. the mousebutton has been released.

          * The plus-sign ('+'), which follows is always fixed.

          * The next digit (in the range 0 to 7) encodes the modifier keys press
ed,
            where 1 stands for shift, 2 stands for alt and 4 stands for ctrl.

          * The next four digits (e.g. 0028) contain the x-position, where the
            mousebutton has been pressed.

          * The comma to follow is always fixed.

          * The last four digits (e.g. 0061) contain the y-position, where the
            mousebutton has been pressed.

        All those fields are of fixed length, so you may use functions like mid$
 to
        extract certain fields. However, note that with mousex, mousey, mouseb a
nd
        mousemod there are specialized functions to return detailed information 
about
        the mouseclick. Finally it should be noted, that inkey$ will only regist
er
        mouseclicks within the graphic-window; mouseclicks in the text-window ca
nnot be
        detected.

        inkey$ accepts an optional argument, specifying a timeout in seconds; if
 no key
        has been pressed within this span of time, an empty string is returned. 
If the
        timeout-argument is omitted, inkey$ will wait for ever.

        Example

        clear screen
        open window 100,100
        print "Press any key or press 'q' to stop."
        repeat
          a$=inkey$
          print a$
        until(a$="q")

        This program simply returns the key pressed. You may use it, to learn, w
hich
        strings are returned for the special keys on your keyboard (e.g.
        function-keys).

        See also

        clear screen,mousex, mousey, mouseb, mousemod

        ------------------------------------------------------------------------
-------

        Name

        input ? read input from the user (or from a file) and assign it to a var
iable

        Synopsis

        input a
        input a,b,c
        input a$
        input "Hello" a
        input #1 a$

        Description

        input reads the new contents of one or many (numeric- or string-) variab
les,
        either from the keyboard (i.e. from you) or from a file. An optional fir
st
        string-argument specifies a prompt, which will be issued before reading 
any
        contents.

        If you want to read from an open file, you need to specify a hash ('#'),
        followed by the number, under which the file has been opened.

        Note, that the input is split at spaces, i.e. if you enter a whole line
        consisting of many space-separated word, the first input-statement will 
only
        return the first word; the other words will only be returned on subseque
nt
        calls to input; the same applies, if a single input reads multiple varia
bles:
        The first variable gets only the first word, the second one the second w
ord,
        and so on. If you don't like this behaviour, you may use line input, whi
ch
        returns a whole line (including embedded spaces) at once.

        Example

        input "Please enter the name of a file to read: " a$
        open 1,a$
        while(!eof(1))
          input #1 b$
          print b$
        wend

        If this program is stored within a file test.yab and you enter this name
 when
        prompted for a file to read, you will see this output:

        Please enter the name of a file to read: t.yab
        input
        "Please
        enter
        the
        name
        of
        a
        file
        to
        read:
        "
        a$
        open
        1,a$
        while(!eof(1))
        input
        #1
        b$
        print
        b$
        wend

        See also

        line input

        ------------------------------------------------------------------------
-------

        Name

        instr() ? searches its second argument within the first; returns its pos
ition
        if found

        Synopsis

        print instr(a$,b$)
        if (instr(a$,b$)) ?
        pos=instr(a$,b$,x)

        Description

        The instr-functions requires two string arguments and searches the secon
d
        argument within the first. If the second argument can be found within th
e
        first, the position is returned (counting from one). If it can not be fo
und,
        the instr-function returns 0; this makes this function usable within the
        condition of an if-statement (see the example below).

        If you supply a third, numeric argument to the instr-function, it will b
e used
        as a starting point for the search. Therefore instr("abcdeabcdeabcde","e
",8)
        will return 10, because the search for an "e" starts at position 8 and f
inds
        the "e" at position 10 (and not the one at position 5).

        Example

        input "Please enter a text containing the string 'cat': " a$
        if (instr(a$,"cat")) then
          print "Well done !"
        else
          print "No cat in your input ..."
        endif

        See also

        rinstr

        ------------------------------------------------------------------------
-------

        Name

        int() ? return the integer part of its single numeric argument

        Synopsis

        print int(a)

        Description

        The int-function returns only the digits before the comma; int(2.5) retu
rns 2
        and int(-2.3) returns -2.

        Example

        input "Please enter a whole number between 1 and 10: " a
        if (a=int(a) and a>=1 and a<=10) then
          print "Thanx !"
        else
          print "Never mind ..."
        endif

        See also

        frac, floor, ceil

        L

        label ? mark a specific location within your program for goto, gosub or 
restore
        left$() ? return (or change) left end of a string
        len() ? return the length of a string
        line ? draw a line
        line input ? read in a whole line of text and assign it to a variable
        local ? mark a variable as local to a subroutine
        log() ? compute the natural logarithm
        loop ? marks the end of an infinite loop
        lower$() ? convert a string to lower case
        ltrim$() ? trim spaces at the left end of a string

        Name

        label ? mark a specific location within your program for goto, gosub or 
restore

        Synopsis

        label foo

        ?

        goto foo

        Description

        The label-command can be used to give a name to a specific location with
in your
        program. Such a position might be referred from one of three commands: g
oto,
        gosub and restore.

        You may use labels safely within libraries, because a label (e.g. foo) d
oes not
        collide with a label with the same name within the main program or withi
n
        another library; yabasic will not mix them up.

        As an aside, please note, that line numbers are a special (however depre
cated)
        case of labels; see the second example below.

        Example

        for a=1 to 100
          if (ran(10)>5) goto done
        next a
        label done

        10 for a=1 to 100
        20   if (ran(10)>5) goto 40
        30 next a
        40

        Within this example, the for-loop will probably be left prematurely with
 a
        goto-statement. This task is done twice: First with labels and then agai
n with
        line numbers.

        See also

        gosub, goto.

        ------------------------------------------------------------------------
-------

        Name

        left$() ? return (or change) left end of a string

        Synopsis

        print left$(a$,2)
        left$(b$,3)="foobar"

        Description

        The left$-function accepts two arguments (a string and a number) and ret
urns
        the part from the left end of the string, whose length is specified by i
ts
        second argument. Loosely spoken, it simply returns the requested number 
of
        chars from the left end of the given string.

        Note, that the left$-function can be assigned to, i.e. it may appear on 
the
        left hand side of an assignment. In this way it is possible to change a 
part of
        the variable used within the left$-function. Note, that that way the len
gth of
        the string cannot be changed, i.e. characters might be overwritten, but 
not
        added. For an example see below.

        Example

        input "Please answer yes or no: " a$
        l=len(a$):a$=lower$(a$):print "Your answer is ";
        if (left$("yes",l)=a$ and l>=1) then
          print "yes"
        elsif (left$("no",l)=a$ and l>=1) then
          print "no"
        else
          print "?"
        endif

        This example asks a simple yes/no question and goes some way to accept e
ven
        incomplete input, while still being able to reject invalid input.

        This second example demonstrates the capability to assign to the
        left$-function.

        a$="Heiho World !"
        print a$
        left$(a$,5)="Hello"
        print a$

        See also

        right$, mid$

        ------------------------------------------------------------------------
-------

        Name

        len() ? return the length of a string

        Synopsis

        x=len(a$)

        Description

        The len-function returns the length of its single string argument.

        Example

        input "Please enter a password: " a$
        if (len(a$)<6) error "Password too short !"

        This example checks the length of the password, that the user has entere
d.

        See also

        left$, right$ and mid$,

        ------------------------------------------------------------------------
-------

        Name

        line ? draw a line

        Synopsis

        open window 100,100
        line 0,0,100,100
        line 0,0 to 100,100
        new curve
        line 100,100
        line to 100,100

        open window 100,100
        clear line 0,0,100,100
        clear line 0,0 to 100,100
        new curve
        clear line 100,100
        clear line to 100,100

        Description

        The line-command draws a line. Simple as this is, the line-command has a
 large
        variety of forms as they are listed in the synopsis above. Lets look at 
them a
        little closer:

          * A line has a starting and an end point; therefore the line-command
            (normally) needs four numbers as arguments, representing these two p
oints.
            This is the first form appearing within the synopsis.

          * You may separate the two points with either ',' or to, which account
s for
            the second form of the line-command.

          * The line-command may be used to draw a connected sequence of lines w
ith a
            sequence of commands like line x,y; Each command will draw a line fr
om the
            point where the last line-command left off, to the point specified i
n the
            arguments. Note, that you need to use the command new curve before y
ou may
            issue such a line-command. See the example below.

          * You may insert the word to for beauty: line to x,y, which does exact
ly the
            same as line x,y

          * Finally, you may choose not to draw, but to erase the lines; this ca
n be
            done by prepending the phrase clear. This account for all the other 
forms
            of the line-command.

        Example

        open window 200,200
        line 10,10 to 10,190
        line 10,190 to 190,190
        new curve
        for a=0 to 360
          line to 10+a*180/360,100+60*sin(a*pi/180)
        next a

        This example draws a sine-curve (with an offset in x- and y-direction). 
Note,
        that the first line-command after new curve does not draw anything. Only
 the
        coordinates will be stored. The second iteration of the loop then uses t
hese
        coordinates as a starting point for the first line.

        See also

        new curve, close curve, open window

        ------------------------------------------------------------------------
-------

        Name

        line input ? read in a whole line of text and assign it to a variable

        Synopsis

        line input a
        line input a$
        line input "Hello" a
        line input #1 a$

        Description

        In most respects line input is like the input-command: It reads the new
        contents of a variable, either from keyboard or from a file. However, li
ne
        input always reads a complete line and assigns it to its variable. line 
input
        does not stop reading at spaces and is therefore the best way to read in
 a
        string which might contain whitespace. Note, that the final newline is s
tripped
        of.

        Example

        line input "Please enter your name (e.g. Frodo Beutelin): " a$
        print "Hello ",a$

        Note that the usage of line input is essential in this example; a simple
        input-statement would only return the string up to the first space, e.g.
 Frodo.

        See also

        input

        ------------------------------------------------------------------------
-------

        Name

        local ? mark a variable as local to a subroutine

        Synopsis

        sub foo()

          local a,b,c$,d(10),e$(5,5)

          ?

        end sub

        Description

        The local-command can (and should be) used to mark a variable (or array)
 as
        local to the containing subroutine. This means, that a local variable in
 your
        subroutine is totally different from a variable with the same name withi
n your
        main program. Variables which are known everywhere within your program a
re
        called global in contrast.

        Declaring variables within the subroutine as local helps to avoid hard t
o find
        bugs; therefore local variables should be used whenever possible.

        Note, that the parameters of your subroutines are always local.

        As you may see from the example, local arrays may be created without usi
ng the
        keyword dim (which is required only for global arrays).

        Example

        a=1
        b=1
        print a,b
        foo()
        print a,b

        sub foo()
          local a
          a=2
          b=2
        end sub

        This example demonstrates the difference between local and global variab
les; it
        produces this output:

        1 1
        1 2

        As you may see, the content of the global variable a is unchanged after 
the
        subroutine foo; this is because the assignment a=2 within the subroutine
        affects the local variable a only and not the global one. However, the v
ariable
        b is never declared local and therefore the subroutine changes the globa
l
        variable, which is reflected in the output of the second print-statement
.

        See also

        sub, static, dim

        ------------------------------------------------------------------------
-------

        Name

        log() ? compute the natural logarithm

        Synopsis

        a=log(x)
        a=log(x,base)

        Description

        The log-function computes the logarithm of its first argument. The optio
nal
        second argument gives the base for the logarithm; if this second argumen
t is
        omitted, the euler-constant 2.71828? will be taken as the base.

        Example

        open window 200,200
        for x=10 to 190 step 10:for y=10 to 190 step 10
          r=3*log(1+x,1+y)
          if (r>10) r=10
          if (r<1) r=1
          fill circle x,y,r
        next y:next x

        This draws another nice plot.

        See also

        exp

        ------------------------------------------------------------------------
-------

        Name

        loop ? marks the end of an infinite loop

        Synopsis

        do
          ?
        loop

        Description

        The loop-command marks the ends of a loop (which is started by do), wher
ein all
        statements within the loop are repeated forever. In this respect the do
        loop-loop is infinite, however, you may leave it anytime via break or go
to.

        Example

        print "Hello, I will throw dice, until I get a 2 ..."
        do
          r=int(ran(6))+1
          print r
          if (r=2) break
        loop

        See also

        do, for, repeat, while, break

        ------------------------------------------------------------------------
-------

        Name

        lower$() ? convert a string to lower case

        Synopsis

        l$=lower$(a$)

        Description

        The lower$-function accepts a single string-argument and converts it to 
all
        lower case.

        Example

        input "Please enter a password: " a$
        if (a$=lower$(a$)) error "Your password is NOT mixed case !"

        This example prompts for a password and checks, if it is really lower ca
se.

        See also

        upper$

        ------------------------------------------------------------------------
-------

        Name

        ltrim$() ? trim spaces at the left end of a string

        Synopsis

        a$=ltrim$(b$)

        Description

        The ltrim$-function removes all whitespace from the left end of a string
 and
        returns the result.

        Example

        input "Please answer 'yes' or 'no' : " a$
        a$=lower$(ltrim$(rtrim$(a$)))
        if (len(a$)>0 and a$=left$("yes",len(a$))) then
          print "Yes ..."
        else
          print "No ..."
        endif

        This example prompts for an answer and removes any spaces, which might p
recede
        the input; therefore it is even prepared for the (albeit somewhat pathol
ogical
        case, that the user first hits space before entering his answer.

        See also

        rtrim$, trim$

        M

        max() ? return the larger of its two arguments
        mid$() ? return (or change) characters from within a string
        min() ? return the smaller of its two arguments
        mod ? compute the remainder of a division
        mouseb ? extract the state of the mousebuttons from a string returned by
 inkey$
        mousemod ? return the state of the modifier keys during a mouseclick
        mousex ? return the x-position of a mouseclick
        mousey ? return the y-position of a mouseclick

        Name

        max() ? return the larger of its two arguments

        Synopsis

        print max(a,b)

        Description

        Return the maximum of its two arguments.

        Example

        dim m(10)
        for a=1 to 1000
          m=0
          For b=1 to 10
            m=max(m,ran(10))
          next b
          m(m)=m(m)+1
        next a

        for a=1 to 9
          print a,": ",m(a)
        next a

        Within the inner for-loop (the one with the loop-variable b), the exampl
e
        computes the maximum of 10 random numbers. The outer loop (with the loop
        variable a) now repeats this process 1000 times and counts, how often ea
ch
        maximum appears. The last loop finally reports the result.

        Now, the interesting question would be, which will be approached, when w
e
        increase the number of iterations from thousand to infinity. Well, maybe
        someone could just tell me :-)

        See also

        min

        ------------------------------------------------------------------------
-------

        Name

        mid$() ? return (or change) characters from within a string

        Synopsis

        print mid$(a$,2,1)
        print mid$(a$,2)
        mid$(a$,5,3)="foo"
        mid$(a$,5)="foo"

        Description

        The mid$-function requires three arguments: a string and two numbers, wh
ere the
        first number specifies a position within the string and the second one g
ives
        the number of characters to be returned; if you omit the second argument
, the
        mid$-function returns all characters up to the end of the string.

        Note, that you may assign to the mid$-function, i.e. mid$ may appear on 
the
        left hand side of an assignment. In this way it is possible to change a 
part of
        the variable used within the mid$-function. Note, that that way the leng
th of
        the string cannot be changed, i.e. characters might be overwritten, but 
not
        added. For an example see below.

        Example

        input "Please enter a string: " a$
        for a=1 to len(a$)
          if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
        next a
        print "When you turn everything to lower case and"
        print "replace every vowel with 'e', your input reads:"
        print
        print a$

        This example transforms the input string a bit, using the mid$-function 
to
        retrieve a character from within the string as well as to change it.

        See also

        left$ and right$.

        ------------------------------------------------------------------------
-------

        Name

        min() ? return the smaller of its two arguments

        Synopsis

        print min(a,b)

        Description

        Return the minimum of its two argument.

        Example

        dim m(10)
        for a=1 to 1000
          m=min(ran(10),ran(10))
          m(m)=m(m)+1
        next a

        for a=1 to 9
          print a,": ",m(a)
        next a

        For each iteration of the loop, the lower of two random number is record
ed. The
        result is printed at the end.

        See also

        max

        ------------------------------------------------------------------------
-------

        Name

        mod ? compute the remainder of a division

        Synopsis

        print mod(a,b)

        Description

        The mod-function divides its two arguments and computes the remainder. N
ote,
        that a/b-int(a/b) and mod(a,b) are always equal.

        Example

        clear screen
        print at(10,10) "Please wait ";
        p$="-\|/"
        for a=1 to 100
          rem  ... do something lengthy here, or simply sleep :-)
          pause(1)
          print at(22,10) mid$(p$,1+mod(a,4))
        next a

        This example executes some time consuming action within a loop (in fact,
 it
        simply sleeps) and gives the user some indication of progress by display
ing a
        turning bar (that's where the mod-function comes into play).

        See also

        int, frac

        ------------------------------------------------------------------------
-------

        Name

        mouseb ? extract the state of the mousebuttons from a string returned by
 inkey$

        Synopsis

        inkey$
        print mouseb()
        print mouseb
        a$=inkey$
        print mouseb(a$)

        Description

        The mouseb-function is a helper function for decoding part of the (rathe
r
        complicated) strings, which are returned by the inkey$-function. If a
        mousebutton has been pressed, the mouseb-function returns the number (1,
2 or 3)
        of the mousebutton, when it is pressed and returns its negative (-1,-2 o
r -3),
        when it is released.

        The mouseb-function accepts zero or one arguments. A single argument sho
uld be
        a string returned by the inkey$-function; if mouseb is called without an
y
        arguments, it returns the values from the last call to inkey$, which are
 stored
        implicitly and internally by yabasic.

        Note

        Note however, that the value returned by the mouseb-function does not re
flect
        the current state of the mousebuttons. It rather extracts the informatio
n from
        the string passed as an argument (or from the last call to the inkey$-fu
nction,
        if no argument is passed). So the value returned by mouseb reflects the 
state
        of the mousebuttons at the time the inkey$-function has been called; as 
opposed
        to the time the mouseb-function is called.

        Example

        open window 200,200
        clear screen
        print "Please draw lines; press (and keep it pressed)"
        print "the left mousebutton for the starting point,"
        print "release it for the end-point."
        do
          if (mouseb(release$)=1) press$=release$
          release$=inkey$
          if (mouseb(release$)=-1) then
            line mousex(press$),mousey(press$) to mousex(release$),mousey(releas
e$)
          endif
        loop

        This is a maybe the most simplistic line-drawing program possible, catch
ing
        presses as well as releases of the first mousebutton.

        See also

        inkey$, mousex, mousey and mousemod

        ------------------------------------------------------------------------
-------

        Name

        mousemod ? return the state of the modifier keys during a mouseclick

        Synopsis

        inkey$
        print mousemod()
        print mousemod
        a$=inkey$
        print mousemod(a$)

        Description

        The mousemod-function is a helper function for decoding part of the (rat
her
        complicated) strings, which are returned by the inkey$-function if a
        mousebutton has been pressed. It returns the state of the keyboard modif
iers
        (shift, ctrl or alt): If the shift-key is pressed, mousemod returns 1, f
or the
        alt-key 2 and for the ctrl-key 4. If more than one key is pressed, the s
um of
        these values is returned, e.g. mousemod returns 5, if shift and ctrl are
        pressed simultaneously.

        The mousemod-function accepts zero or one arguments. A single argument s
hould
        be a string returned by the inkey$-function; if mousemod is called witho
ut any
        arguments, it returns the values from the last call to inkey$ (which are
 stored
        implicitly and internally by yabasic).

        Note

        Please see also the Note within the mouseb-function.

        Example

        open window 200,200
        clear screen
        do
          a$=inkey$
          if (left$(a$,2)="MB") then
            x=mousex(a$)
            y=mousey(a$)
            if (mousemod(a$)=0) then
              circle x,y,20
            else
              fill circle x,y,20
            endif
          endif
        loop

        This program draws a circle, whenever a mousebutton is pressed; the circ
les are
        filled, when any modifier is pressed, and empty if not.

        See also

        inkey$, mousex, mousey and mouseb

        ------------------------------------------------------------------------
-------

        Name

        mousex ? return the x-position of a mouseclick

        Synopsis

        inkey$
        print mousex()
        print mousex
        a$=inkey$
        print mousex(a$)

        Description

        The mousex-function is a helper function for decoding part of the (rathe
r
        complicated) strings, which are returned by the inkey$-function; It retu
rns the
        x-position of the mouse as encoded within its argument.

        The mousex-function accepts zero or one arguments. A single argument sho
uld be
        a string returned by the inkey$-function; if mousex is called without an
y
        arguments, it returns the values from the last call to inkey$ (which are
 stored
        implicitly and internally by yabasic).

        Note

        Please see also the Note within the mouseb-function.

        Example

        open window 200,200
        clear screen
        do
          a$=inkey$
          if (left$(a$,2)="MB") then
            line mousex,0 to mousex,200
          endif
        loop

        This example draws vertical lines at the position, where the mousebutton
 has
        been pressed.

        See also

        inkey$, mousemod, mousey and mouseb

        ------------------------------------------------------------------------
-------

        Name

        mousey ? return the y-position of a mouseclick

        Synopsis

        inkey$
        print mousey()
        print mousey
        a$=inkey$
        print mousey(a$)

        Description

        The mousey-function is a helper function for decoding part of the (rathe
r
        complicated) strings, which are returned by the inkey$-function. mousey 
returns
        the y-position of the mouse as encoded within its argument.

        The mousey-function accepts zero or one arguments. A single argument sho
uld be
        a string returned by the inkey$-function; if mousey is called without an
y
        arguments, it returns the values from the last call to inkey$ (which are
 stored
        implicitly and internally by yabasic).

        Note

        Please see also the Note within the mouseb-function.

        Example

        open window 200,200
        clear screen
        do
          a$=inkey$
          if (left$(a$,2)="MB") then
            line 0,mousey to 200,mousey
          endif
        loop

        This example draws horizontal lines at the position, where the mousebutt
on has
        been pressed.

        See also

        inkey$, mousemod, mousex and mouseb

        N

        new curve ? start a new curve, that will be drawn with the line-command
        next ? mark the end of a for loop
        not ? negate an expression; can be written as !
        numparams ? return the number of parameters, that have been passed to a
            subroutine

        Name

        new curve ? start a new curve, that will be drawn with the line-command

        Synopsis

        new curve
        line to x,y

        Description

        The new curve-function starts a new sequence of lines, that will be draw
n by
        repeated line to-commands.

        Example

        open window 200,200
        ellipse(100,50,30,60)
        ellipse(150,100,60,30)
        sub ellipse(x,y,xr,yr)
          new curve
          for a=0 to 2*pi step 0.2
            line to x+xr*cos(a),y+yr*sin(a)
          next a
          close curve
        end sub

        This example defines a subroutine ellipse that draws an ellipse. Within 
this
        subroutine, the ellipse is drawn as a sequence of lines started with the
 new
        curve command and closed with close curve.

        See also

        line, close curve

        ------------------------------------------------------------------------
-------

        Name

        next ? mark the end of a for loop

        Synopsis

        for a=1 to 10
        next a

        Description

        The next-keyword marks the end of a for-loop. All statements up to the
        next-keyword will be repeated as specified with the for-clause. Note, th
at the
        name of the variable is optional; so instead of next a you may write nex
t.

        Example

        for a=1 to 300000
          for b=1 to 21+20*sin(pi*a/20)
            print "*";
          next b
          print
          sleep 0.1
        next a

        This example simply plots a sine-curve until you fall asleep.

        See also

        for

        ------------------------------------------------------------------------
-------

        Name

        not ? negate an expression; can be written as !

        Synopsis

        if (not a<b) then ?
        bad=!okay

        Description

        The keyword not (or ! for short) is mostly used within conditions (e.g. 
within
        if- or while-statements). There it is employed to negate the condition o
r
        expression (i.e. turn TRUE into FALSE and vice versa)

        However not can be used within arithmetic calculations too., simply beca
use
        there is no difference between arithmetic and logical expressions.

        Example

        input "Please enter three ascending numbers: " a,b,c
        if (not (a<b and b<c)) error " the numbers you have entered are not asce
nding ..."

        See also

        and,or

        ------------------------------------------------------------------------
-------

        Name

        numparams ? return the number of parameters, that have been passed to a
        subroutine

        Synopsis

        sub foo(a,b,c)
          if (numparams=1) ?
          ?
        end sub

        Description

        Within a subroutine the local variable numparam or numparams contains th
e
        number of parameters, that have been passed to the subroutine. This info
rmation
        can be useful, because the subroutine may have been called with fewer
        parameters than actually declared. The number of values that actually ha
ve been
        passed while calling the subroutine, can be found in numparams.

        Note, that arguments which are used in the definition of a subroutine bu
t are
        left out during a call to it (thereby reducing the value of numparams) r
eceive
        a value of 0 or "" (empty string) respectively.

        Example

        a$="123456789"
        print part$(a$,4)
        print part$(a$,3,7)

        sub part$(a$,f,t)
          if (numparams=2) then
            return mid$(a$,f)
          else
            return mid$(a$,f,t-f+1)
          end if
        end sub

        When you run this example, it will print 456789 and 34567. Take a look a
t the
        subroutine part$, which returns part of the string which has been passed
 as an
        argument. If (besides the string) two numbers are passed, they define th
e
        starting and end position of the substring, that will be returned. Howev
er, if
        only one number is passed, the rest of the string, starting from this po
sition
        will be returned. Each of these cases is recognized with the help of the
        numparams variable.

        See also

        sub

        O

        on gosub ? jump to one of multiple gosub-targets
        on goto ? jump to one of many goto-targets
        on interrupt ? change reaction on keyboard interrupts
        open ? open a file
        open printer ? open printer for printing graphics
        open window ? open a graphic window
        logical or ? logical or, used in conditions
        or() ? arithmetic or, used for bit-operations

        Name

        on goto ? jump to one of multiple gosub-targets

        Synopsis

        on a gosub foo,bar,baz
          ?
        label foo
          ?
        return

        label bar
          ?
        return

        label baz
          ?
        return

        Description

        The on gosub statement uses its numeric argument (the one between on and
 gosub)
        to select an element from the list of labels, which follows after the
        gosub-keyword: If the number is 1, the program does a gosub to the first
 label;
        if the number is 2, to the second and, so on. if the number is zero or l
ess,
        the program continues at the position of the first label; if the number 
is
        larger than the total count of labels, the execution continues at the po
sition
        of the last label; i.e. the first and last label in the list constitute 
some
        kind of fallback-slot.

        Note, that the on gosub-command can no longer be considered state of the
 art;
        people (not me !) may even start to mock you, if you use it.

        Example

        do
          print "Please enter a number between 1 and 3: "
          print
          input "Your choice " a
          on a gosub bad,one,two,three,bad
        loop

        label bad
          print "No. Please between 1 and 3"
        return

        label one
          print "one"
        return

        label two
          print "two"
        return

        label three
          print "three"
        return

        Note, how invalid input (a number less than 1, or larger than 3) is
        automatically detected.

        See also

        goto, on gosub/function>

        ------------------------------------------------------------------------
-------

        Name

        on goto ? jump to one of many goto-targets

        Synopsis

        on a goto foo,bar,baz
          ?
        label foo
          ?
        label bar
          ?
        label baz
          ?

        Description

        The on goto statement uses its numeric argument (the one between on and 
goto to
        select an element from the list of labels, which follows after the
        goto-keyword: If the number is 1, the execution continues at the first l
abel;
        if the number is 2, at the second, and so on. if the number is zero or l
ess,
        the program continues at the position of the first label; if the number 
is
        larger than the total count of labels, the execution continues at the po
sition
        of the last label; i.e. the first and last label in the list constitute 
some
        kind of fallback-slot.

        Note, that (unlike the goto-command) the on goto-command can no longer b
e
        considered state of the art; people may (not me !) even start to mock yo
u, if
        you use it.

        Example

        label over
        print "Please Select one of these choices: "
        print
        print "  1 -- show time"
        print "  2 -- show date"
        print "  3 -- exit"
        print
        input "Your choice " a
        on a goto over,show_time,show_date,terminate,over

        label show_time
          print time$()
        goto over

        label show_date
          print date$()
        goto over

        label terminate
        exit

        Note, how invalid input (a number less than 1, or larger than 3) is
        automatically detected; in such a case the question is simply issued aga
in.

        See also

        goto, on gosub/function>

        ------------------------------------------------------------------------
-------

        Name

        on interrupt ? change reaction on keyboard interrupts

        Synopsis

        on interrupt break
        ?
        on interrupt continue

        Description

        With the on interrupt-command you may change the way, how yabasic reacts
 on a
        keyboard interrupt; it comes in two variants: on interrupt break and on
        interrupt continue. A keyboard interrupt is produced, if you press ctrl-
C on
        your keyboard; normally (and certainly after you have called on interrup
t
        break), yabasic will terminate with an error message. However after the 
command
        on interrupt continue yabasic ignores any keyboard interrupt. This may b
e
        useful, if you do not want your program being interruptible during certa
in
        critical operations (e.g. updating of files).

        Example

        print "Please stand by while writing a file with random data ..."
        on interrupt continue
        open "random.data" for writing as #1
        for a=1 to 100
          print #1 ran(100)
          print a," percent done."
          sleep 1
        next a
        close #1
        on interrupt continue

        This program writes a file with 100 random numbers. The on interrupt con
tinue
        command insures, that the program will not be terminated on a keyboard
        interrupt and the file will be written entirely in any case. The sleep-c
ommand
        just stretches the process artificially to give you a chance to try a ct
rl-C.

        See also

        There is no related command.

        ------------------------------------------------------------------------
-------

        Name

        open ? open a file

        Synopsis

        open a,"file","r"
        open #a,"file","w"
        open #a,printer
        open "file" for reading as a
        open "file" for writing as #a
        a=open("file")
        a=open("file","r")
        if (open(a,"file")) ?
        if (open(a,"file","w")) ?

        Description

        The open-command opens a file for reading or writing or a printer for pr
inting
        text. open comes in a wide variety of ways; it requires these arguments:

        filenumber

            In the synopsis this is a or #a. In yabasic each file is associated 
with a
            number between 1 and a maximum value, which depends on the operating
            system. For historical reasons the filenumber can be preceded by a h
ash ('#
            '). Note, that specifying a filenumber is optional; if it is omitted
, the
            open-function will return a filenumber, which should then be stored 
in a
            variable for later reference. This filenumber can be a simple number
 or an
            arbitrary complex arithmetic expression, in which case braces might 
be
            necessary to save yabasic from getting confused.

        filename

            In the synopsis above this is "file". This string specifies the name
 of the
            file to open (note the important caveat on specifying these filename
s).

        accessmode

            In the synopsis this is "r", "w", for reading or for writing. This s
tring
            or clause specifies the mode in which the file is opened; it may be 
one of:

            "r"

                Open the file for reading (may also be written as for reading). 
If the
                file does not exist, the command will fail. This mode is the def
ault,
                i.e. if no mode is specified with the open-command, the file wil
l be
                opened with this mode.

            "w"

                Open the file for writing (may also be written as for writing). 
If the
                file does not exist, it will be created.

            "a"

                Open the file for appending, i.e. what you write to the file wil
l be
                appended after its initial contents. If the file does not exist,
 it
                will be created.

            "b"

                This letter may not appear alone, but may be combined with the o
ther
                letters (e.g. "rb") to open a file in binary mode (as opposed to
 text
                mode).

        As you may see from the synopsis, the open-command may either be called 
as a
        command (without braces) or as a function (with braces). If called as a
        function, it will return the filenumber or zero if the operation fails.
        Therefore the open-function may be used within the condition of an
        if-statement.

        If the open-command fails, you may use peek("error") to retrieve the exa
ct
        nature of the error.

        Furthermore note, that there is another, somewhat separate usage of the
        open-command; if you specify the bareword printer instead of a filename,
 the
        command opens a printer for printing text. Every text (and only text) yo
u print
        to this file will appear on your printer. Note, that this is very differ
ent
        from printing graphics, as can be done with open printer.

        Example

        open "foo.bar" for writing as #1
        print #1 "Hallo !"
        close #1
        if (not open(1,"foo.bar")) error "Could not open 'foo.bar' for reading"
        while(not eof(1))
          line input #1 a$
          print a$
        wend

        This example simply opens the file foo.bar, writes a single line, reopen
s it
        and reads its contents again.

        See also

        close, print, peek, peek("error") and open printer

        ------------------------------------------------------------------------
-------

        Name

        open printer ? open printer for printing graphics

        Synopsis

        open printer
        open printer "file"

        Description

        The open printer-command opens a printer for printing graphics. The comm
and
        requires, that a graphic window has been opened before. Everything that 
is
        drawn into this window will then be sent to the printer too.

        A new piece of paper may be started with the clear window-command; the f
inal
        (or only) page will appear after the close printer-command.

        Note, that you may specify a filename with open printer; in that case th
e
        printout will be sent to a filename instead to a printer. Your program o
r the
        user will be responsible for sending this file to the printer afterwards
.

        If you use yabasic under Unix, you will need a postscript printer (becau
se
        yabasic produces postscript output). Alternatively you may use ghostscri
pt to
        transform the postscript file into a form suitable for your printer; but
 that
        is beyond the responsibility of yabasic.

        Example

        open window 200,200
        open printer
        line 0,0 to 200,200
        text 100,100,"Hallo"
        close window
        close printer

        This example will open a window, draw a line and print some text within;
        everything will appear on your printer too.

        See also

        close printer

        ------------------------------------------------------------------------
-------

        Name

        open window ? open a graphic window

        Synopsis

        open window x,y
        open window x,y,"font"

        Description

        The open window-command opens a window of the specified size. Only one w
indow
        can be opened at any given moment of time.

        An optional third argument specifies a font to be used for any text with
in the
        window. It can however be changed with any subsequent text-command.

        Example

        for a=200 to 400 step 10
          open window a,a
          for b=0 to a
            line 0,b to a,b
            line b,0 to b,a
          sleep 0.1
          close window
        next a

        See also

        close window, text

        ------------------------------------------------------------------------
-------

        Name

        or ? logical or, used in conditions

        Synopsis

        if (a or b) ?
        while (a or b) ?

        Description

        Used in conditions (e.g within if or while) to join two expressions. Ret
urns
        true, if either its left or its right or both arguments are true; return
s false
        otherwise.

        Example

        input "Please enter a number"
        if (a>9 or a<1) print "a is not between 1 and 9"

        See also

        and,not

        ------------------------------------------------------------------------
-------

        Name

        or() ? arithmetic or, used for bit-operations

        Synopsis

        x=or(a,b)

        Description

        Used to compute the bitwise or of both its argument. Both arguments are 
treated
        as binary numbers (i.e. a series of 0 and 1); a bit of the resulting val
ue will
        then be 1, if any of its arguments has 1 at this position in their binar
y
        representation.

        Note, that both arguments are silently converted to integer values and t
hat
        negative numbers have their own binary representation and may lead to
        unexpected results when passed to or.

        Example

        print or(14,3)

        This will print 15. This result is clear, if you note, that the binary
        representation of 14 and 3 are 1110 and 0011 respectively; this will yie
ld 1111
        in binary representation or 15 as decimal.

        See also

        oand, eor and not

        P

        pause ? pause, sleep, wait for the specified number of seconds
        peek ? retrieve various internal information
        peek$ ? retrieve various internal string-information
        pi ? a constant with the value 3.14159
        poke ? change selected internals of yabasic
        print ? Write to terminal or file
        print color ? print with color
        print colour ? see print color
        putbit ? draw a rectangle of pixels encoded within a string into the gra
phics
            window
        putscreen ? draw a rectangle of characters into the text terminal

        Name

        pause ? pause, sleep, wait for the specified number of seconds

        Synopsis

        pause 5

        Description

        The pause-command has many different names: You may write pause, sleep o
r wait
        interchangeably; whatever you write, yabasic will always do exactly the 
same.

        The pause-command will simply wait for the specified number of seconds. 
This
        may be a fractional number, so you may well wait less than a second. How
ever,
        if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds
, 0.01
        seconds, 0.001 seconds and so on) you will find that at some point yabas
ic will
        not wait at all. The minimal interval that can be waited depends on the 
system
        (Unix, Windows) you are using.

        The pause-command cannot be interrupted. However, sometimes you may want
 the
        wait to be interruptible by simply pressing a key on the keyboard. In su
ch
        cases you should consider using the inkey$-function, with a number of se
conds
        as an argument).

        Example

        deg=0
        do
          maxx=44+40*sin(deg)
          for x=1 to maxx
            print "*";
          next x
          pause 0.1+(maxx*maxx/(4*84*84))
          print
          deg=deg+0.1
        loop

        This example draws a sine-curve; due to the pause-statement the speed of
        drawing varies in the same way as the speed of a ball might vary, if it 
would
        roll along this curve under the influence of gravity.

        See also

        sleep, wait

        ------------------------------------------------------------------------
-------

        Name

        peek ? retrieve various internal information

        Synopsis

        print peek("foo")
        a=peek(#1)

        Description

        The peek-function has many different and mostly unrelated uses. It is a 
kind of
        grab-bag for retrieving all kinds of numerical information, internal to 
yabasic
        . The meaning of the numbers returned be the peek-function depends on th
e
        string or number passed as an argument.

        peek always returns a number, however the closely related peek$-function
        exists, which may be used to retrieve string information from among the
        internals of yabasic. Finally note, that some of the values which are re
trieved
        with peek may even be changed, using the poke-function.

        There are two variants of the peek-function: One expects an integer, pos
itive
        number and is described within the first entry of the list below. The ot
her
        variant expects one of a well defined set of strings as described in the
 second
        and all the following entries of the list below.

        peek(a)

            Read a single character from the file a (which must be open of cours
e).

        peek("argument")

            Return the number of arguments, that have been passed to yabasic at
            invocation time. E.g. if yabasic has been called like this: yabasic 
foo.yab
            bar baz, then peek("argument") will return 2. This is because foo.ya
b is
            treated as the name of the program to run, whereas bar and baz are
            considered arguments to the program, which are passed on the command
 line.
            Note, that for windows-users, who tend to click on the icon (as oppo
sed to
            starting yabasic on the command line), this peekwill mostly return 0
.

            The function peek("argument") can be written as peek("arguments") to
o.

            You will want to check out the corresponding function peek$("argumen
t") to
            actually retrieve the arguments. Note, that each call to peek$("argu
ment")
            reduces the number returned by peek("argument").

        peek("error")

            Return a number specifying the nature of the last error in an open- 
or
            seek-statement. Normally an error within an open-statement immediate
ly
            terminates your program with an appropriate error-message, so there 
is no
            chance and no need to learn more about the nature of the error. Howe
ver, if
            you use open as a condition (e.g. if (open(#1,"foo")) ?) the outcome
            (success or failure) of the open-operation will determine, if the co
ndition
            evaluates to true or false. If now such an operation fails, your pro
gram
            will not be terminated and you might want to learn the reason for fa
ilure.
            This reason will be returned by peek("error") (as a number) or by pe
ek$
            ("error") (as a string)

            The table below shows the various error codes; the value returned by
 peek$
            ("error") explains the nature of the error. Note, that the codes 10,
11 and
            12 refer to the seek-command.

            Table 7.1. Error codes

            +-------------------------------------------------------------------
------+
            |  peek   |peek$("error")|                  Explanation             
      |
            |("error")|              |                                          
      |
            |---------+--------------+------------------------------------------
------|
            |    2    |Stream already|Do not try to open one and the same filenu
mber  |
            |         |in use        |twice; rather close it first.             
      |
            |---------+--------------+------------------------------------------
------|
            |         |'x' is not a  |The optional filemode argument, which may 
be    |
            |    3    |valid filemode|passed to the open-function, has an invali
d     |
            |         |              |value                                     
      |
            |---------+--------------+------------------------------------------
------|
            |    4    |could not open|The open-call did not work, no further    
      |
            |         |'foo'         |explanation is available.                 
      |
            |---------+--------------+------------------------------------------
------|
            |         |reached       |You have opened more files than your opera
ting  |
            |    5    |maximum number|system permits.                           
      |
            |         |of open files |                                          
      |
            |---------+--------------+------------------------------------------
------|
            |         |cannot open   |The commands open printer and open #1,prin
ter   |
            |         |printer:      |both open a printer (refer to their descri
ption |
            |    6    |already       |for the difference). However, only one can
 be   |
            |         |printing      |active at a time; if you try to do both at
 the  |
            |         |graphics      |same time, you will receive this error.   
      |
            |---------+--------------+------------------------------------------
------|
            |    7    |could not open|Well, it simply did not work.             
      |
            |         |line printer  |                                          
      |
            |---------+--------------+------------------------------------------
------|
            |    9    |invalid stream|An attempt to use an invalid (e.g. negativ
e)    |
            |         |number        |stream number; example: open(-1,"foo")    
      |
            |---------+--------------+------------------------------------------
------|
            |         |could not     |                                          
      |
            |   10    |position      |seek did not work.                        
      |
            |         |stream x to   |                                          
      |
            |         |byte y        |                                          
      |
            |---------+--------------+------------------------------------------
------|
            |   11    |stream x not  |You have tried to seek within a stream, th
at has|
            |         |open          |not been opened yet.                      
      |
            |---------+--------------+------------------------------------------
------|
            |         |seek mode 'x' |The argument, which has been passed to see
k is  |
            |   12    |is none of    |invalid.                                  
      |
            |         |begin,end,here|                                          
      |
            +-------------------------------------------------------------------
------+

        peek("fontheight")

            Return the height of the font used within the graphic window. If non
e is
            open, this peek will return the height of the last font used or 10, 
if no
            window has been opened yet.

        peek("screenheight")

            Return the height in characters of the window, wherein yabasic runs.
 If you
            have not called clear screen yet, this peekwill return 0, regardless
 of the
            size of your terminal.

        peek("screenwidth")

            Return the width in characters of the window, wherein yabasic runs. 
If you
            have not called clear screen yet, this peekwill return 0, regardless
 of the
            size of your terminal.

        peek("secondsrunning")

            Return the number of seconds that have passed since the start of yab
asic.

        peek("millisrunning")

            Return the number of milliseconds, that have passed since the start 
of
            yabasic.

        peek("version")

            Return the version number of yabasic, e.g. 2.77. See also the relate
d peek$
            ("version"), which returns nearly the same information (plus the
            patchlevel) as a string, e.g. "2.77.1".

        peek("winheight")

            Return the height of the graphic-window in pixels. If none is open, 
this
            peek will return the height of the last window opened or 100, if non
e has
            been opened yet.

        peek("winwidth")

            Return the width of the graphic-window in pixels. If none is open, t
his
            peek will return the width of the last window opened or 100, if none
 has
            been opened yet.

        peek("isbound")

            Return true, if the executing yabasic-program is part of a standalon
e
            program; see the section about creating a standalone-program for det
ails.

        peek("version")

            Return the version number of yabasic (e.g. 2.72).

        Example

        open "foo" for reading as #1
        open "bar" for writing as #2
        while(not eof(#1))
          poke #2,chr$(peek(#1));
        wend

        This program will copy the file foo byte by byte to bar.

        Note, that each peek does something entirely different, and only one has
 been
        demonstrated above. Therefore you need to make up examples yourself for 
all the
        other peeks.

        See also

        peek$, poke, open

        ------------------------------------------------------------------------
-------

        Name

        peek$ ? retrieve various internal string-information

        Synopsis

        print peek$("foo")

        Description

        The peek$-function has many different and unrelated uses. It is a kind o
f
        grab-bag for retrieving all kinds of string information, internal to yab
asic;
        the exact nature of the strings returned be the peek$-function depends o
n the
        string passed as an argument.

        peek$ always returns a string, however the closely related peek-function
        exists, which may be used to retrieve numerical information from among t
he
        internals of yabasic. Finally note, that some of the values which are re
trieved
        with peek$ may even be changed, using the poke-function.

        The following list shows all possible arguments to peek$:

        peek$("infolevel")

            Returns either "debug", "note", "warning", "error" or "fatal", depen
ding on
            the current infolevel. This value can be specified with an option on
 the
            command line or changed during the execution of the program with the
            corresponding poke; however, normally only the author of yabasic (me
 !)
            would want to change this from its default value "warning".

        peek$("textalign")

            Returns one of nine possible strings, specifying the default alignme
nt of
            text within the graphics-window. The alignment-string returned by th
is peek
            describes, how the text-command aligns its string-argument with resp
ect to
            the coordinates supplied. However, this value does not apply, if the
            text-command explicitly specifies an alignment. Each of these string
s is
            two characters long. The first character specifies the horizontal al
ignment
            and can be either l, r or c, which stand for left, right or center. 
The
            second character specifies the vertical alignment and can be one of 
t, b or
            c, which stand for top, bottom or center respectively.

            You may change this value with the corresponding command poke
            "textalign",?; the initial value is lb, which means the top of the l
eft and
            the top edge if the text will be aligned with the coordinates, that 
are
            specified within the text-command.

        peek$("windoworigin")

            This peek returns a two character string, which specifies the positi
on of
            the origin of the coordinate system of the window; this string might
 be
            changed with the corresponding command poke "windoworigin",x,y or sp
ecified
            as the argument of the origin command; see there for a detailed desc
ription
            of the string, which might be returned by this peek.

        peek$("program_name")

            Returns the name of the yabasic-program that is currently executing;
            typically this is the name, that you have specified on the commandli
ne, but
            without any path-components. So this peek$ might return foo.yab. As 
a
            special case when yabasic has been invoked without the name of a pro
gram to
            be executed this peek will return the literal strings standard input
 or,
            when also the option -e has been specified, command line. See also p
eek$
            ("program_file_name") and peek$("interpreter_path") for related
            information.

        peek$("program_file_name")

            Returns the full file-name of the yabasic-program that is currently
            executing; typically this is the name, that you have specified on th
e
            commandline, including any path-components. For the special case, th
at you
            have bound your yabasic-program with the interpreter to a single sta
ndalone
            executable, this peek$ will return its name. See also peek$("program
_name")
            and peek$("interpreter_path") for related information.

        peek$("interpreter_path")

            Return the full file-name of the yabasic-interpreter that is current
ly
            executing your program; typically this will end on yabasic or yabasi
c.exe
            depending on your platform and the path will be where you installed 
yabasic
            . For bound programs (see creating a standalone-program) however, th
is may
            be different and will include whatever you specified during the bind
            -command.

            See also peek$("program_name") and peek$("program_file_name") for re
lated
            information. Employing these, it would be possible for a yabasic-pro
gram to
            start itself: system(peek$("interpreter_path") + " " + peek$
            ("program_file_name")). Of course, in this simple form this would be
 a bad
            idea, because this would start concurrent instances of yabasic witho
ut end.

        peek$("error")

            Return a string describing the nature of the last error in an open- 
or
            seek-statement. See the corresponding peek("error") for a detailed
            description.

        peek$("library")

            Return the name of the library, this statement is contained in. See 
the
            import-command for a detailed description or for more about librarie
s.

        peek$("version")

            Version of yabasic as a string; e.g. 2.77.1. See also the related pe
ek
            ("version"), which returns nearly the same information (minus the
            patchlevel) as a number, e.g. 2.77.

        peek$("os")

            This peek returns the name of the operating system, where your progr
am
            executes. This can be either windows or unix.

        peek$("font")

            Return the name of the font, which is used for text within the graph
ic
            window; this value can be specified as the third argument to the ope
n
            window-command.

        peek$("env","NAME")

            Return the environment variable specified by NAME (which may be any 
string
            expression). Which kind of environment variables are available on yo
ur
            system depends, as well as their meaning, on your system; however ty
ping
            env on the command line will produce a list (for Windows and Unix al
ike).
            Note, that peek$("env",...) can be written as peek$("environment",..
.) too.

        peek$("argument")

            Return one of the arguments, that have been passed to yabasic at inv
ocation
            time (the next call will return the the second argument, and so on).
 E.g.
            if yabasic has been called like this: yabasic foo.yab bar baz, then 
the
            first call to peek$("argument") will return bar. This is because foo
.yab is
            treated as the name of the program to run, whereas bar and baz are
            considered arguments to this program, which are passed on the comman
d line.
            The second call to peek$("argument") will return baz. Note, that for
            windows-users, who tend to click on the icon (as opposed to starting
            yabasic on the command line), this peekwill mostly return the empty 
string.

            Note, that peek$("argument") can be written as peek$("arguments").

            Finally you will want to check out the corresponding function peek
            ("argument").

        Example

        print "You have supplied these arguments: "
        while(peek("argument"))
          print peek("argument"),peek$("argument")
        wend

        If you save this program in a file foo.yab and execute it via yabasic t.
yab a b
        c (for windows users: please use the command line for this), your will g
et this
        output:

        3a
        2b
        1c

        See also

        peek, poke, open

        ------------------------------------------------------------------------
-------

        Name

        pi ? a constant with the value 3.14159

        Synopsis

        print pi

        Description

        pi is 3.14159265359 (well at least for yabasic); do not try to assign to
 pi
        (e.g. pi=22/7) this would not only be mathematically dubious, but would 
also
        result in a syntax error.

        Example

        for a=0 to 180
          print "The sine of ",a," degrees is ",sin(a*pi/180)
        next a

        This program uses pi to transform an angle from degrees into radians.

        See also

        euler

        ------------------------------------------------------------------------
-------

        Name

        poke ? change selected internals of yabasic

        Synopsis

        poke "foo","bar"
        poke "foo",baz
        poke #a,"bar"
        poke #a,baz

        Description

        The poke-command may be used to change details of yabasic's behaviour. L
ike the
        related function peek, poke does many different things, depending on the
        arguments supplied.

        Here are the different things you can do with poke:

        poke 5,a

            Write the given byte (a in the example above) to the specified strea
m (5#a
            in the example).

            See also the related function function peek(1).

        poke "dump","filename.dump"

            Dump the internal form of your basic-program to the named file; this
 is
            only useful for debugging the internals of yabasic itself.

            The second argument ("filename.dump" in the example) should be the n
ame of
            a file, that gets overwritten with the dump, please be careful.

        poke "fontheight",12

            This poke changes the default fontheight. This can only have an effe
ct, if
            the fonts given in the commands text or open window do not specify a
            fontheight on their own.

        poke "font","fontname"

            This poke specifies the default font. This can only have an effect, 
if you
            do not supply a fontname with the commands text or open window.

        poke "infolevel","debug"

            Change the amount of internal information, that yabasic outputs duri
ng
            execution.

            The second argument can be either "debug", "note", "warning", "error
" or
            "fatal". However, normally you will not want to change this from its
            default value "warning".

            See also the related peek$("infolevel").

        poke "random_seed",42

            Set the seed for the random number generator; if you do this, the ra
n
            -function will return the same sequence of numbers every time the pr
ogram
            is started.

        poke "stdout","some text"

            Send the given text to standard output. Normally one would use print
 for
            this purpose; however, sending e.g. control characters to your termi
nal is
            easier with this poke.

        poke "textalign","cc"

            This poke changes the default alignment of text with respect to the
            coordinates supplied within the text-command. However, this value do
es not
            apply, if the text-command explicitly specifies an alignment. The se
cond
            argument ("cc" in the example) must always be two characters long; t
he
            first character can be one of l (left), r (right) or c (center); the
 second
            character can be either t (top), b (bottom) or c (center); see the
            corresponding peek$("textalign") for a detailed description of this
            argument.

        poke "windoworigin","lt"

            This poke moves the origin of the coordinate system of the window to
 the
            specified position. The second argument ("lt" in the example) must a
lways
            be two characters long; the first character can be one of l (left), 
r (
            right) or c (center); the second character can be either t (top), b 
(bottom
            ) or c (center). Together those two characters specify the new posit
ion of
            the coordinate-origin. See the corresponding peek$("windoworigin") f
or a
            more in depth description of this argument.

        Example

        print "Hello, now you will see, how much work"
        print "a simple for-loop involves ..."
        input "Please press return " a$
        poke "infolevel","debug"
        for a=1 to 10:next a

        This example only demonstrates one of the many pokes, which are describe
d
        above: The program switches the infolevel to debug, which makes yabasic 
produce
        a lot of debug-messages during the subsequent for-loop.

        See also

        peek, peek$

        ------------------------------------------------------------------------
-------

        Name

        print ? Write to terminal or file

        Synopsis

        print "foo",a$,b
        print "foo",a$,b;
        print #a "foo",a$
        print #a "foo",a$;
        print foo using "##.###"
        print reverse "foo"
        print at(10,10) a$,b
        print @(10,10) a$,b
        print color("red","blue") a$,b
        print color("magenta") a$,b
        print color("green","yellow") at(5,5) a$,b

        Description

        The print-statement outputs strings or characters, either to your termin
al
        (also known as console) or to an open file.

        To understand all those uses of the print-statement, let's go through th
e
        various lines in the synopsis above:

        print "foo",a$,b

            Print the string foo as well as the contents of the variables a$ and
 b onto
            the screen, silently adding a newline.

        print "foo",a$,b;

            (Note the trailing semicolon !) This statement does the same as the 
one
            above; only the implicit newline is skipped, which means that the ne
xt
            print-statement will append seamlessly.

        print #a "foo",a$

            This is the way to write to files. The file with the number a must b
e open
            already, an implicit newline is added. Note the file-number #a, whic
h
            starts with a hash ('#') amd is separated from the rest of the state
ment by
            a space only. The file-number (contained in the variable a) must hav
e been
            returned by a previous open-statement (e.g. a=open("bar")).

        print #a "foo",a$;

            The same as above, but without the implicit newline.

        print foo using "##.###"

            Print the number foo with as many digits before and after the decima
l dot
            as given by the number of '#'-signs. See the entries for using and s
tr$ for
            a detailed description of this format.

        print reverse "foo"

            As all the print-variants to follow, this form of the print-statemen
t can
            only be issued after clear screen has been called. The strings and n
umbers
            after the reverse-clause are simply printed inverse (compared to the
 normal
            print-statement).

        print at(10,10) a$,b

            Print at the specified (x,y)-position. This is only allowed after cl
ear
            screen has been called. You may want to query peek$("screenwidth") o
r peek$
            ("screenheight") to learn the actual size of your screen. You may ad
d a
            semicolon to suppress the implicit newline.

        print @(10,10) a$,b

            This is exactly the same as above, however, at may be written as @.

        print color("red","blue") at(5,5) a$,b

            Print with the specified fore- ("red") and background ("blue") color
 (or
            colour). The possible values are "black", "white", "red", "blue", "g
reen",
            "yellow", "cyan" or "magenta". Again, you need to call clear screen 
first
            and add a semicolon if you want to suppress the implicit newline.

        print color("magenta") a$,b

            You may specify the foreground color only.

        print color("green","yellow") a$,b

            A color and a position (in this sequence, not the other way around) 
may be
            specified at once.

        Example

        clear screen
        columns=peek("screenwidth")
        lines=peek("screenheight")
        dim col$(7)
        for a=0 to 7:read col$(a):next a
        data "black","white","red","blue","green","yellow","cyan","magenta"

        for a=0 to 2*pi step 0.1
          print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*
cos(a)+0.9)/2) "*"
          i=i+1
        next a

        This example draws a colored ellipse within the text window.

        See also

        at, print color, input, clear screen, using, ;

        ------------------------------------------------------------------------
-------

        Name

        print color ? print with color

        Synopsis

        print color(fore$) text$
        print color(fore$,back$) text$

        Description

        Not a separate command, but part of the print-command; may be included j
ust
        after print and can only be issued after clear screen has been executed.

        color() takes one or two string-arguments, specifying the color of the t
ext and
        (optionally) the background.

        The one or two strings passed to color() can be one of these: "black", "
white",
        "red", "blue", "green", "yellow", "cyan" and "magenta" (which can be
        abbreviated as "bla", "whi", "red", "blu", "gre", "yel", "cya" and "mag"
        respectively).

        color() can only be used, if clear scren has been issued at least once.

        Note, that color() can be written as colour() too.

        Example

        clear screen
        dim col$(7):for a=0 to 7:read col$(a):next a
        do
          print color(col$(ran(7)),col$(ran(7))) " Hallo ";
          pause 0.01
        loop
        data "black","white","red","blue"
        data "green","yellow","cyan","magenta"

        This prints the word " Hallo " in all colors across your screen.

        See also

        print, clear screen, at

        ------------------------------------------------------------------------
-------

        Name

        print colour ? see print color

        Synopsis

        print colour(fore$) text$
        print colour(fore$,back$) text$

        See also

        color

        ------------------------------------------------------------------------
-------

        Name

        putbit ? draw a rectangle of pixels encoded within a string into the gra
phics
        window

        Synopsis

        open window 200,200
        ?
        a$=getbit(20,20,50,50)
        ?
        putbit a$,30,30
        putbit a$ to 30,30
        putbit a$,30,30,"or"

        Description

        The putbit-command is the counterpart of the getbit$-function. putbit re
quires
        a string as returned by the getbit-function. Such a string contains a re
ctangle
        from the graphic window; the putbit-function puts such a rectangular reg
ion
        back into the graphic-window.

        Note, that the putbit-command currently accepts a fourth argument. Howev
er only
        the string value "or" is supported here. The effect is, that only those 
pixel,
        which are set in the string will be set in the graphic window. Those pix
els,
        which are not set in the string, will not change in the window (as oppos
ed to
        being cleared).

        Example

        c$="rgb 21,21:0000000000000000000000000000000000000000000000000000000000
000032c8000000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c800
00000000000000000000000000000000000000000000000000000000000032c80032c80032c80032
c80032c80032c80032c80032c80032c80032c80032c80032c8000000000000000000000000000000
0000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800
32c80032c80032c80032c80032c80000000000000000000000000000000032c80032c80032c80032
c80032c80032c80032c80032c8c8ff000032c80032c80032c80032c80032c80032c80032c8000000
0000000000000000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8
ff00c8ff00c8ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032
c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c8
0032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8
ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032
c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00
c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8
ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000
000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00
c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c80032c8c8
ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032
c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00
c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c800
32c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032
c80032c80032c80032c80000000000000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00
c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c800000000000000
00000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032
c80032c80032c80032c80032c80000000000000000000000000032c80032c80032c80032c80032c8
0032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800000000000000
00000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032
c80032c80032c80032c80032c80032c80000000000000000000000000000000000000000000032c8
0032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800000000000000
00000000000000000000000000000000000000000000000000000032c80032c80032c80032c80032
c80032c80032c80032c80032c8000000000000000000000000000000000000000000000000000000
00000000000000000000000000000000000000000000000000000000000000000000000000000000
0000000000000000000000000000"

        open window 200,200

        do
          x=ran(220)-10
          y=ran(220)-10
          putbit c$,x,y,"transparent"
        loop

        This program uses a precanned string (containing the image of a blue cir
cle
        with a yellow centre) and draws it repeatedly into the graphic-window. T
he mode
        "transparent" ensures, that no pixels will be cleared.

        There are two possible values for the third argument of putbit. Both mod
es
        differ in the way, they replace (or not) any pixels from the window with
 pixels
        from the bitmap having the background colour.

        transparent or t

            With this mode the pixels from the window will be kept, if the bitma
p
            contains pixels with background colour at this position; i.e. the bi
tmap is
            transparent

        solid or s

            With this mode the pixels from the window will be overpainted with t
he
            pixels from the bitmap in any case; i.e. the bitmap is solid

        If you omit this argument, the default transparent applies.

        See also

        getbit$, open window

        ------------------------------------------------------------------------
-------

        Name

        putscreen ? draw a rectangle of characters into the text terminal

        Synopsis

        clear screen
        ?
        a$=getscreen$(5,5,10,10)
        ?
        putscreen a$,7,7

        Description

        The putscreen-command is the counterpart of the getscreen$-function. put
screen
        requires a string as returned by the getscreen-function. Such a string c
ontains
        a rectangular detail from the terminal; the putscreen-function puts such
 a
        region back into the terminal-window.

        Note, that clear screen must have been called before.

        Example

        clear screen
        for a=1 to 200
          print color("red") "Hallo !";
          print color("blue") "Welt !";
        next a
        r$=getscreen$(0,0,20,20)
        for x=0 to 60
          putscreen r$,x,0
          sleep 0.1
        next x

        This example prints the string "Hallo !Welt !" all over the screen and t
hen
        moves a rectangle from one side to the other.

        See also

        getscreen$, clear screen

        R

        ran() ? return a random number
        read ? read data from data-statements
        rectangle ? draw a rectangle
        redim ? create an array prior to its first use. A synonym for dim
        rem ? start a comment
        repeat ? start a repeat-loop
        restore ? reposition the data-pointer
        return ? return from a subroutine or a gosub
        reverse ? print reverse (background and foreground colors exchanged)
        right$() ? return (or change) the right end of a string
        rinstr() ? find the rightmost occurrence of one string within the other
        rtrim$() ? trim spaces at the right end of a string

        Name

        ran() ? return a random number

        Synopsis

        print ran()
        x=ran(y)

        Description

        The ran-function returns a random number. If no argument is given, the n
umber
        returned is in the range from 0 to 1; where only 0 is a possible value; 
1 will
        never be returned. If an argument is supplied, the number returned will 
be in
        the range from 0 up to this argument, whereas this argument itself is no
t a
        possible return value. Regardless of the range, ran is guaranteed to hav
e
        exactly 2**30 different return values.

        If you call ran multiple times during your program, the sequence of rand
om
        numbers will be different each time you invoke your program; however, if
, e.g.
        for testing you prefer to always have the same sequence of random number
s you
        may issue poke "random_seed",123.

        Example

        clear screen
        c=peek("screenwidth")-1
        l=peek("screenheight")

        dim col$(8)
        for a=0 to 7:read col$(a):next a
        data "black","white","red","blue","green","yellow","cyan","magenta"

        do
          x=ran(c)
          y=l-ran(l*exp(-32*((x/c-1/2)**2)))
          i=i+1
          print color(col$(mod(i,8))) at(x,y) "*";
        loop

        This example will print a colored bell-curve.

        See also

        int

        ------------------------------------------------------------------------
-------

        Name

        read ? read data from data-statements

        Synopsis

        read a$,a
        ?
        data "Hello !",7

        Description

        The read-statement retrieves literal data, which is stored within
        data-statements elsewhere in your program.

        Example

        read num
        dim col$(num)
        for a=1 to num:read col$(a):next a
        clear screen
        print "These are the colours known to yabasic:\n"
        for a=1 to num
          print colour(col$(a)) col$(a)
        next a

        data 8,"black","white","red","blue"
        data "green","yellow","cyan","magenta"

        This program prints the names of the colors known to yabasic in those ve
ry
        colors.

        See also

        data, restore

        ------------------------------------------------------------------------
-------

        Name

        rectangle ? draw a rectangle

        Synopsis

        open window 100,100
        rectangle 10,10 to 90,90
        rectangle 20,20,80,80
        rect 20,20,80,80
        box 30,30,70,70
        clear rectangle 30,30,70,70
        fill rectangle 40,40,60,60
        clear fill rectangle 60,60,40,40

        Description

        The rectangle-command (also known as box or rect, for short) draws a rec
tangle;
        it accepts four parameters: The x- and y-coordinates of two facing corne
rs of
        the rectangle. With the optional clauses clear and fill (which may appea
r
        together and in any sequence) the rectangle can be cleared and filled
        respectively.

        Example

        open window 200,200
        c=1
        do
          for phi=0 to pi step 0.1
            if (c) then
              rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),10
0-100*cos(phi)
            else
              clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(p
hi),100-100*cos(phi)
            endif
            sleep 0.1
          next phi
          c=not c
        loop

        This example draws a nice animated pattern; watch it for a couple of hou
rs, to
        see how it develops.

        See also

        open window, open printer, line, circle, triangle

        ------------------------------------------------------------------------
-------

        Name

        redim ? create an array prior to its first use. A synonym for dim

        Synopsis

        See the dim-command.

        Description

        The redim-command does exactly the same as the dim-command; it is just a
        synonym. redim has been around in older versions of basic (not even yaba
sic)
        for many years; therefore it is supported in yabasic for compatibility r
easons.

        Please refer to the entry for the dim-command for further information.

        ------------------------------------------------------------------------
-------

        Name

        rem ? start a comment

        Synopsis

        rem  Hey, this is a comment
        #    the hash-sign too (at beginning of line)
        // even the double slash
        ' and the single quote (at beginning of line)
        print "Not a comment" #    This is an error !!
        print "Not a comment"://   But this is again a valid comment
        print "Not a comment" //   even this.
        print "Not a comment" rem  and this !

        Description

        rem introduces a comment (like # or //), that extends up to the end of t
he
        line.

        Those comments do not even need a colon (':') in front of them; they (re
m, #, '
        (single quite) and //) all behave alike except for # and ', which may on
ly
        appear at the very beginning of a line; therefore the fourth example in 
the
        synopsis above (print "Not a comment" # This is an error !!) is indeed a
n
        error.

        Note, that rem is an abbreviation for remark. remark however is not a va
lid
        command in yabasic.

        Finally note, that a comment introduced with '#' may have a special mean
ing
        under unix; see the entry for # for details.

        Example

        #
        rem   comments on data structures
        #     are more useful than
        //    comments on algorithms.
        rem

        This program does nothing, but in a splendid and well commented way.

        See also

        #, //

        ------------------------------------------------------------------------
-------

        Name

        repeat ? start a repeat-loop

        Synopsis

        repeat
          ?
        until (?)

        Description

        The repeat-loop executes all the statements up to the final until-keywor
d over
        and over. The loop is executed as long as the condition, which is specif
ied
        with the until-clause, becomes true. By construction, the statements wit
hin the
        loop are executed at least once.

        Example

        x=0
        clear screen
        print "This program will print the numbers from 1 to 10"
        repeat
          x=x+1
          print x
          print "Press any key for the next number, or 'q' to quit"
          if (inkey$="q") break
        until(x=10)

        This program is pretty much useless, but self-explanatory.

        See also

        until, break, while, do

        ------------------------------------------------------------------------
-------

        Name

        restore ? reposition the data-pointer

        Synopsis

        read a,b,c,d,e,f
        restore
        read g,h,i
        restore foo
        data 1,2,3
        label foo
        data 4,5,6

        Description

        The restore-command may be used to reset the reading of data-statements,
 so
        that the next read-statement will read data from the first data-statemen
t.

        You may specify a label with the restore-command; in that case, the next
        read-statement will read data starting at the given label. If the label 
is
        omitted, reading data will begin with the first data-statement within yo
ur
        program.

        Example

        input "Which language (german/english) ? " l$
        if (instr("german",l$)>0) then
          restore german
        else
          restore english
        endif

        for a=1 to 3
          read x,x$
          print x,"=",x$
        next a

        label english
        data 1,"one",2,"two",3,"three"
        label german
        data 1,"eins",2,"zwei",3,"drei"

        This program asks to select one of those languages known to me (i.e. eng
lish or
        german) and then prints the numbers 1,2 and 3 and their textual equivale
nts in
        the chosen language.

        See also

        read, data, label

        ------------------------------------------------------------------------
-------

        Name

        return ? return from a subroutine or a gosub

        Synopsis

        gosub foo
        ?
        label foo
        ?
        return

        sub bar(baz)
          ?
          return quertz
        end sub

        Description

        The return-statement serves two different (albeit somewhat related) purp
oses.
        The probably more important use of return is to return control from with
in a
        subroutine to the place in your program, where the subroutine has been c
alled.
        If the subroutine is declared to return a value, the return-statement mi
ght be
        accompanied by a string or number, which constitutes the return value of
 the
        subroutine.

        However, even if the subroutine should return a value, the return-statem
ent
        need not carry a value; in that case the subroutine will return 0 or the
 empty
        string (depending on the type of the subroutine). Moreover, feel free to
 place
        multiple return-statements within your subroutine; it's a nice way of
        controlling the flow of execution.

        The second (but historically first) use of return is to return to the po
sition,
        where a prior gosub has left off. In that case return may not carry a va
lue.

        Example

        do
          read a$
          if (a$="") then
            print
            end
          endif
          print mark$(a$)," ";
        loop

        data "The","quick","brown","fox","jumped"
        data "over","the","lazy","dog",""

        sub mark$(a$)
          if (instr(lower$(a$),"q")) return upper$(a$)
          return a$
        end sub

        This example features a subroutine mark$, that returns its argument in u
pper
        case, if it contains the letter "q", or unchanged otherwise. In the test
-text
        the word quick will end up being marked as QUICK.

        The example above demonstrates return within subroutines; please see gos
ub for
        an example of how to use return in this context.

        See also

        sub, gosub

        ------------------------------------------------------------------------
-------

        Name

        reverse ? print reverse (background and foreground colors exchanged)

        Synopsis

        clear screen
        ?
        print reverse "foo"

        Description

        reverse may be used to print text in reverse. reverse is not a separate
        command, but part of the print-command; it may be included just after th
e print
        and can only be issued once that clear screen has been issued.

        Example

        clear screen

        print "1 ";
        c=3
        do
          prim=true
          for a=2 to sqrt(c)
            if (frac(c/a)=0) then
              prim=false
              break
            endif
          next a
          if (prim) then
            print
            print reverse c;
          else
            print c;
          endif
          print " ";
          c=c+1
        loop

        This program prints numbers from 1 on and marks each prime number in rev
erse.

        See also

        at, print color, print, clear screen

        ------------------------------------------------------------------------
-------

        Name

        right$() ? return (or change) the right end of a string

        Synopsis

        print right$(a$,2)
        right$(b$,2)="baz"

        Description

        The right$-function requires two arguments (a string and a number) and r
eturns
        the part from the right end of the string, whose length is specified by 
its
        second argument. So, right$ simply returns the requested number of chars
 from
        the right end of the given string.

        Note, that the right$-function can be assigned to, i.e. it may appear on
 the
        left hand side of an assignment. In this way it is possible to change a 
part of
        the variable used within the right$-function. Note, that that way the le
ngth of
        the string cannot be changed, i.e. characters might be overwritten, but 
not
        added. For an example see below.

        Example

        print "Please enter a length either in inch or centimeter"
        print "please add 'in' or 'cm' to mark the unit."
        input "Length: " a$
        if (right$(a$,2)="in") then
           length=val(a$)*2.56
        elsif (right$(a$,2)="cm") then
           length=val(a$)
        else
           error "Invalid input: "+a$
        endif

        This program allows the user to enter a length qualified with a unit (ei
ther
        inch or centimeter).

        This second example demonstrates the capability to assign to the
        right$-function.

        a$="Heiho World !"
        print a$
        right$(a$,7)="dwarfs."
        print a$

        See also

        right$ and mid$

        ------------------------------------------------------------------------
-------

        Name

        rinstr() ? find the rightmost occurrence of one string within the other

        Synopsis

        pos=rinstr("Thequickbrownfox","equi")
        pos=rinstr(a$,b$,x)

        Description

        The rinstr-function accepts two string-arguments and tries to find the s
econd
        within the first. However, unlike the instr, the rinstr-function finds t
he
        rightmost (or last) occurrence of the string; whereas the instr-function
 finds
        the leftmost (or first) occurrence. In any case however, the position is
        counted from the left.

        If you supply a third, numeric argument to the rinstr-function, it will 
be used
        as a starting point for the search. Therefore rinstr("abcdeabcdeabcde","
e",8)
        will return 5, because the search for an "e" starts at position 8 and fi
nds the
        first one at position 5.

        Example

        print rinstr("foofoofoobar","foo")

        This simple example will print 7, because it finds the rightmost among t
he
        three occurrences of foo within the string. Note, that

        print instr("foofoofoobar","foo")

        would have printed 1.

        See also

        instr

        ------------------------------------------------------------------------
-------

        Name

        rtrim$() ? trim spaces at the right end of a string

        Synopsis

        a$=rtrim$(b$)

        Description

        The rtrim$-function removes all whitespace from the right end of a strin
g and
        returns the result.

        Example

        open 1,"foo"
        dim lines$(100)
        l=1
        while(not eof(1))
          input #1 a$
          a$=rtrim$(a$)
          if (right$(line$,1)="\\") then
            line$=line$+" "+a$
          else
            lines$(l)=line$
            l=l+1
            line$=a$
          endif
        end while
        print "Read ",l," lines"

        This example reads the file foo allowing for continuation lines, which a
re
        marked by a \, which appears as the last character on a line. For conven
ience
        whitespace at the right end of a line is trimmed with rtrim.

        See also

        ltrim$, trim$

        S

        screen ? as clear screen clears the text window
        seek() ? change the position within an open file
        sig() ? return the sign of its argument
        sin() ? return the sine of its single argument
        sleep ? pause, sleep, wait for the specified number of seconds
        split() ? split a string into many strings
        sqr() ? compute the square of its argument
        sqrt() ? compute the square root of its argument
        static ? preserves the value of a variable between calls to a subroutine
        step ? specifies the increment step in a for-loop
        str$() ? convert a number into a string
        sub ? declare a user defined subroutine
        switch ? select one of many alternatives depending on a value
        system() ? hand a statement over to your operating system and return its
            exitcode
        system$() ? hand a statement over to your operating system and return it
s
            output

        Name

        screen ? as clear screen clears the text window

        Synopsis

        clear screen

        Description

        The keyword screen appears only within the sequence clear screen; please
 see
        there for a description.

        See also

        clear screen

        ------------------------------------------------------------------------
-------

        Name

        seek() ? change the position within an open file

        Synopsis

        open 1,"foo"
        seek #1,q
        seek #1,x,"begin"
        seek #1,y,"end"
        seek #1,z,"here"

        Description

        The seek-command changes the position, where the next input (or peek) st
atement
        will read from an open file. Usually files are read from the beginning t
o the
        end sequentially; however sometimes you may want to depart from this sim
ple
        scheme. This can be done with the seek-command, allowing you to change t
he
        position, where the next piece of data will be read from the file.

        seek accepts two or three arguments: The first one is the number of an a
lready
        open file. The second one is the position where the next read from the f
ile
        will start. The third argument is optional and specifies the the point f
rom
        where the position (the second argument) will count. It can be one of:

        begin

            Count from the beginning of the file.

        end

            Count from the end of the file.

        here

            Count from the current position within the file.

        Example

        open #1,"count.dat","w"
        for a=1 to 10
          print #1,"00000000";
          if (a<10) print #1,";";
        next a

        dim count(10)
        do
          x=int(ran(10))
          i=i+1
          if (mod(i,1000)=0) print ".";
          count(x)=count(x)+1
          curr$=right$("00000000"+str$(count(x)),8)
          seek #1,9*x,"begin"
          print #1,curr$;
        loop

        This example increments randomly one of ten counters (in the array count
());
        however, the result is always kept and updated within the file count.dat
, so
        even in case of an unexpected interrupt, the result will not be lost.

        See also

        tell, open, print, peek

        ------------------------------------------------------------------------
-------

        Name

        sig() ? return the sign of its argument

        Synopsis

        a=sig(b)

        Description

        Return +1, -1 or 0, if the single argument is positive, negative or zero
.

        Example

        clear screen
        dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
        do
          num=ran(100)-50
          print color(c$(2+sig(num))) num
        loop

        This program prints an infinite sequence of random number; positive numb
ers are
        printed in green, negative numbers are printed red (an exact zero would 
be
        printed white). (With a little extra work, this program could be easily
        extended into a brokerage system)

        See also

        abs, int, frac

        ------------------------------------------------------------------------
-------

        Name

        sin() ? return the sine of its single argument

        Synopsis

        y=sin(angle)

        Description

        The sin-function expects an angle (in radians, not degrees) and returns 
its
        sine.

        Example

        open window 200,200
        new curve
        for phi=0 to 2*pi step 0.1
          line to 100+90*sin(phi),100+90*cos(phi)
        next phi
        close curve

        This program draws a circle (ignoring the existence of the circle-comman
d).

        See also

        asin, cos

        ------------------------------------------------------------------------
-------

        Name

        sleep ? pause, sleep, wait for the specified number of seconds

        Synopsis

        sleep 4

        Description

        The sleep-command has many different names: You may write pause, sleep o
r wait
        interchangeably; whatever you write, yabasic will always do exactly the 
same.

        Therefore you should refer to the entry for the pause-function for furth
er
        information.

        ------------------------------------------------------------------------
-------

        Name

        split() ? split a string into many strings

        Synopsis

        dim w$(10)
        ?
        num=split(a$,w$())
        num=split(a$,w$(),s$)

        Description

        The split-function requires a string (containing the text to be split), 
a
        reference to a string-array (which will receive the resulting strings, i
.e. the
        tokens) and an optional string (with a set of characters, at which to sp
lit,
        i.e. the delimiters).

        The split-function regards its first argument (a string) as a list of to
kens
        separated by delimiters and it will store the list of tokens within the
        array-reference you have supplied. Note, that the array, which is passed
 as a
        reference (w$() in the synopsis), will be resized accordingly, so that y
ou
        don't have to figure out the number of tokens in advance. The element at
        position zero (i.e. w$(0)) will not be used.

        normally (i.e. if you omit the third, which is the delimiter-argument) t
he
        function will regard space or tab as delimiters for tokens; however by
        supplying a third argument, you may split at any single of the character
s
        within this string. E.g. if you supply ":;" as the third argument, then 
colon
        (:) or semicolon (;) will delimit tokens.

        Note, that a sequence of separator-characters will produce a sequence of
 empty
        tokens; that way, the number of tokens returned will always be one plus 
the
        number of separator characters contained within the string. Refer to the
        closely related token-function, if you do not like this behaviour. In so
me way,
        the split-function focuses on the separators (other than the token-funct
ion,
        which focuses on the tokens), hence its name.

        The second argument is a reference on a string-array, where the tokens w
ill be
        stored; this array will be expanded (or shrunk) to have room for all tok
ens, if
        necessary.

        The first argument finally contains the text, that will be split into to
kens.
        The split-function returns the number of tokens that have been found.

        Please see the examples below for some hints on the exact behaviour of t
he
        split-function and how it differs from the token-function:

        Example

        print "This program will help you to understand, how the"
        print "split()-function exactly works and how it behaves"
        print "in certain special cases."
        print
        print "Please enter a line containing tokens separated"
        print "by either '=' or '-'"
        dim t$(10)
        do
          print
          input "Please enter a line: " l$
          num=split(l$,t$(),"=-")
          print num," Tokens: ";
          for a=1 to num
            if (t$(a)="") then
              print "(EMPTY)";
            else
              print t$(a);
            endif
            if (a<num) print ",";
          next a
          print
        loop

        This program prints the following output:

        Please enter a line: a
        1 Tokens: a

        Please enter a line:
        0 Tokens:

        Please enter a line: ab
        1 Tokens: ab

        Please enter a line: a=b
        2 Tokens: a,b

        Please enter a line: a-
        2 Tokens: a,(EMPTY)

        Please enter a line: a-=
        3 Tokens: a,(EMPTY),(EMPTY)

        Please enter a line: =a-
        3 Tokens: (EMPTY),a,(EMPTY)

        Please enter a line: a=-b
        3 Tokens: a,(EMPTY),b

        Please enter a line: a--b-
        4 Tokens: a,(EMPTY),b,(EMPTY)

        Please enter a line: -a==b-c==
        7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)

        See also

        token

        ------------------------------------------------------------------------
-------

        Name

        sqr() ? compute the square of its argument

        Synopsis

        a=sqr(b)

        Description

        The sqr-function computes the square of its numerical argument (i.e. it
        multiplies its argument with itself).

        Example

        for a=1 to 10
          print a,sqr(a),a**2
        next a

        As you may see from the output, sqr can be written as **2 (or ^2) too.

        See also

        sqrt, **, ^

        ------------------------------------------------------------------------
-------

        Name

        sqrt() ? compute the square root of its argument

        Synopsis

        to be written

        Description

        The sqrt-function computes the square root of its numerical argument.

        Example

        for a=1 to 5
          print a,sqrt(a),a**(1/2)
        next a

        As you may see from the output, sqrt can be written as **(1/2) (or ^(1/2
)) too.

        See also

        sqr, **, ^

        ------------------------------------------------------------------------
-------

        Name

        static ? preserves the value of a variable between calls to a subroutine

        Synopsis

        sub foo()

          static a

          ?

        end sub

        Description

        The static keyword can be used within subroutines to mark variables as s
tatic.
        This has two effects: First, the variable is local to the subroutine, i.
e. its
        value is not know outside the subroutine (this is the effect of the loca
l
        keyword). Second, the static-keyword arranges things, so that the variab
le
        keeps its value between invocations of the subroutine (this is different
 from
        the local-keyword).

        Example

        foo()
        foo()
        foo()

        sub foo()
          static a
          local b
          a=a+1
          b=b+1
          print a,b
        end sub

        This program shows the difference between static and local variables wit
hin a
        subroutine; it produces this output:

        1 1
        2 1
        3 1

        The output shows, that the static variable a keeps its value between sub
routine
        calls, whereas b is initialized with the value 0 at every call to the
        subroutine foo.

        See also

        sub, local

        ------------------------------------------------------------------------
-------

        Name

        step ? specifies the increment step in a for-loop

        Synopsis

        for a=1 to 10 step 3
          ?
        next a

        Description

        Specify, by which amount the loop-variable of a for-loop will be increme
nted at
        each step.

        The step (as well as the lower and upper bound) are computed anew in eac
h step;
        this is not common, but possible, as the example below demonstrates.

        Example

        for x=1 to 1000 step y
          y=x+y
          print x," ",y," ";
        next x
        print

        This program computes the fibonacci numbers between 1 and 1000.

        See also

        for

        ------------------------------------------------------------------------
-------

        Name

        str$() ? convert a number into a string

        Synopsis

        a$=str$(a)
        b$=str$(x,"##.###")
        b$=str$(x,"###,###.##")
        b$=str$(x,"###,###.##","_.")

        Description

        The str$-function accepts a numeric argument and returns it as a string.
 This
        conversion between number and string can be controlled with the optional
 third
        argument (the format argument). See the following table of examples to l
earn
        about valid values of this argument. Note, that those examples fall in o
ne of
        two categories: C-style and basic-style; the first 4 examples in the tab
le
        below are C-style, the rest of the examples are basic-style. For more
        information on the C-style formats, you may refer to your favorite
        documentation on the C programming language. The basic-style formats are
 much
        simpler, they just depict the desired output, marking digits with '#'; g
roups
        of (usually three) digits may be separated with colons (','), the decima
l dot
        must be marked by a literal dot ('.'). Moreover these characters (colons
 and
        dot) may be replaced by other characters to satisfy the needs of non-eng
lish
        (e.g. german) languages; see the examples below.

        Note, that for clarity, each space in the result has been replaced by th
e
        letter 'x', because it would be hard to figure out, how many spaces are
        produced exactly otherwise.

        Table 7.2. Examples for the format argument

        +-----------------------------------------------------------------------
------+
        |   Example   | Result for |                                            
      |
        |   string    | converting |                   Description              
      |
        |             |  1000*pi   |                                            
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |The '2' determines the minimum length of the
      |
        |%2.5f        |3141.59265  |output; but if needed (as in the example) th
e     |
        |             |            |output can be longer. The '5' is the number 
of    |
        |             |            |digits after the decimal point.             
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |Two spaces (which appear as 'x') are added t
o pad |
        |%12.5f       |xx3141.59265|the output to the requested length of 12    
      |
        |             |            |characters.                                 
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |The 'g' requests, that the precision ('5')  
      |
        |%012.5g      |0000003141.6|specifies the overall number of digits (befo
re and|
        |             |            |after the decimal point).                   
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |The '-' requests the output to be left-cente
red   |
        |%-12.5f      |3141.59265xx|(therefore the filling space appears at the 
      |
        |             |            |right).                                     
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |Each '#' specifies a digit (either before or
 after|
        |             |            |the dot), the '.' specifies the position of 
the   |
        |#####.##     |x3141.59    |dot. As 1000*pi does not have enough digits,
 the 5|
        |             |            |requested digits before the dot are filled u
p with|
        |             |            |a space (which shows up as an 'x').         
      |
        |-------------+------------+--------------------------------------------
------|
        |##,###.##    |x3,141.59   |Nearly the same as above, but the colon from
 the  |
        |             |            |format shows up within the result.          
      |
        |-------------+------------+--------------------------------------------
------|
        |##,###.## and|            |                                            
      |
        |an additional|x3.141,59   |Similar to the example above, but colon and 
dot   |
        |argument of  |            |are replaced with dot and colon respectively
.     |
        |".,"         |            |                                            
      |
        |-------------+------------+--------------------------------------------
------|
        |##,###.## and|            |Similar to the example above, but colon and 
dot   |
        |an additional|x3_141,59   |are replaced with underscore and colon      
      |
        |argument of  |            |respectively.                               
      |
        |"_,"         |            |                                            
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |The format string does not contain a dot, an
d     |
        |#####        |x3142       |therefore the result does not have any fract
ional |
        |             |            |digits.                                     
      |
        |-------------+------------+--------------------------------------------
------|
        |             |            |As 1000*pi has 4 digits in front of the deci
mal   |
        |##.###       |##.###      |dot and the format only specifies 2, yabasic
 does |
        |             |            |not know what to do; therefore it chooses ju
st to |
        |             |            |reproduce the format string.                
      |
        +-----------------------------------------------------------------------
------+

        Example

        do
          input "Please enter a format string: " f$
          a$=str$(1000*pi,f$)
          for a=1 to len(a$)
            if (mid$(a$,a,1)=" ") mid$(a$,a,1)="x"
          next a
          print a$
        loop

        This is the program, that has been used to get the results shown in the 
table
        above.

        See also

        print, using

        ------------------------------------------------------------------------
-------

        Name

        sub ? declare a user defined subroutine

        Synopsis

        foo(2,"hello")

        ?

        sub foo(bar,baz$)
          ?
          return qux
          ?
        end sub

        Description

        The sub-keyword starts the definition of a user defined subroutine. With
 user
        defined subroutines you are able to somewhat extend yabasic with your ow
n
        commands or functions. A subroutine accepts arguments (numbers or string
s) and
        returns a number or a string (however, you are not required to assign th
e value
        returned to a variable).

        The name of the subroutine follows after the keyword sub. If the name (i
n the
        synopsis: foo) ends on a '$', the subroutine should return a string (wit
h the
        return-statement), otherwise a number.

        After the name of the subroutine yabasic requires a pair of braces; with
in
        those braces you may specify a list of parameters, for which values can 
(but
        need not) be included when calling the subroutine. If you omit one of th
ose
        parameters when calling such a subroutine, it assumes the value zero (fo
r
        numeric parameters) or the empty string (for string-parameters). However
 from
        the special variable numparams you may find out, how many arguments have
 really
        been passed when calling the subroutine.

        Parameters of a subroutine are always local variables (see the keyword l
ocal
        for more explanation).

        From within the subroutine you may return any time with the keyword retu
rn;
        along with the return-keyword you may specify the return value. Note tha
t more
        than one return is allowed within a single subroutine.

        Finally, the keyword end sub ends the subroutine definition. Note, that 
the
        definition of a subroutine need not appear within the program before the
 first
        call to this sub.

        Note

        As braces have two uses in yabasic (i.e. for supplying arguments to a
        subroutine as well as to list the indices of an array). yabasic can not 
tell
        apart an array from a subroutine with the same name. Therefore you canno
t
        define a subroutine with the same name as an array !

        Example

        p=2
        do
          if (is_prime(p)) print p
          p=p+1
        loop

        sub is_prime(a)
          local b
          for b=2 to sqrt(a)
            if (frac(a/b)=0) return false
          next b
          return true
        end sub

        This example is not the recommended way to compute prime numbers. Howeve
r it
        gives a nice demonstration of using a subroutine.

        See also

        local, static, peek

        ------------------------------------------------------------------------
-------

        Name

        switch ? select one of many alternatives depending on a value

        Synopsis

        switch a
          case 1
          case 2
          ?
        end switch

        ?

        switch a$
          case "a"
          case "b"
        end switch

        Description

        The switch-statement selects one of many codepaths depending on a numeri
cal or
        string expression. I.e. it takes an expression (either numeric or string
) and
        compares it with a series of values, each wrapped within a case-clause. 
If the
        expression equals the value given in a case-clause, the subsequent state
ments
        are executed.

        The default-clause allows one to specify commands, which should be execu
ted, if
        none of case-clauses matches.

        Note, that many case-clauses might be clustered (e.g. case "a":case "b":
case
        "c"). Or put another way: You need a break-statement at the end of a
        case-branch, if you do not want to run into the next case.

        Example

        input "Please enter a single digit: " n
        switch n
          case 0:print "zero":break
          case 1:print "one":break
          case 2:print "two":break
          case 3:print "three":break
          case 4:print "four":break
          case 5:case 6: case 7:case 8:case 9
            print "Much !":break
          default:print "Hey ! That was more than a single digit !"
        end switch

        This example translates a single digit into a string; note, how the case
s 5 to
        7 are clustered.

        See also

        switch, case, break

        ------------------------------------------------------------------------
-------

        Name

        system() ? hand a statement over to your operating system and return its
        exitcode

        Synopsis

        ret=system("foo")
        system("bar")

        Description

        The system-command accepts a single string argument, which specifies a c
ommand
        to be executed. The function will return the exitcode of the command; it
s
        output (if any) will be lost.

        Example

        print "Please enter the name of the file, that should be deleted."
        input f$
        if (system("rm "+f$+" >/dev/null 2>&1")) then
          print "Error !"
        else
          print "okay."
        endif

        This program is Unix-specific: It uses the Unix-command rm to remove a f
ile.

        See also

        system$

        ------------------------------------------------------------------------
-------

        Name

        system$() ? hand a statement over to your operating system and return it
s
        output

        Synopsis

        print system$("dir")

        Description

        The system$-command accepts a single string argument, specifying a comma
nd,
        that can be found and executed by your operating system. It returns the 
output
        of this command as one big string.

        Example

        input "Please enter the name of a directory: " d$
        print
        print "This is the contents of the '"+d$+"':"
        print system$("dir "+d$)

        This example lists the contents of a directory, employing the dir-comman
d
        (which is about the only program, that is known under Unix as well as Wi
ndows).

        See also

        system, chomp

        T

        tan() ? return the tangent of its argument
        tell ? get the current position within an open file
        text ? write text into your graphic-window
        then ? tell the long from the short form of the if-statement
        time$ ? return a string containing the current time
        to ? this keyword appears as part of other statements
        token() ? split a string into multiple strings
        triangle ? draw a triangle
        trim$() ? remove leading and trailing spaces from its argument
        true ? a constant with the value of 1

        Name

        tan() ? return the tangent of its argument

        Synopsis

        foo=tan(bar)

        Description

        The tan-function computes the tangent of its arguments (which should be
        specified in radians).

        Example

        for a=0 to 45
          print tan(a*pi/180)
        next a

        This example simply prints the tangent of all angles between 0 and 45 de
grees.

        See also

        atan, sin

        ------------------------------------------------------------------------
-------

        Name

        tell ? get the current position within an open file

        Synopsis

        open #1,"foo"
          ?
        position=tell(#1)

        Description

        The tell-function requires the number of an open file as an argument. It
        returns the position (counted in bytes, starting from the beginning of t
he
        file) where the next read will start.

        Example

        open #1,"foo","w"
        print #1 "Hello World !"
        close #1

        open #1,"foo"
        seek #1,0,"end"
        print tell(#1)
        close 1

        This example (mis)uses tell to get the size of the file. The seek positi
ons the
        file pointer at the end of the file, therefore the call to tell returns 
the
        total length of the file.

        See also

        tell, open

        ------------------------------------------------------------------------
-------

        Name

        text ? write text into your graphic-window

        Synopsis

        text x,y,"foo"
        text x,y,"foo","lb"
        text x,y,"foo","cc","font"
        text x,y,"foo","font","rt"

        Description

        The text-commands displays a text-string (the third argument) at the giv
en
        position (the first two arguments) within an already opened window. The 
font to
        be used can be optionally specified as either the fourth or fifth argume
nt
        ("font" in the example above). A font specified this way will also be us
ed for
        any subsequent text-commands, as long as they do not specify a font them
selves.

        The fourth or fifth optional argument ("lb" in the example above) can be
 used
        to specify the alignment of the text with respect to the specified posit
ion.
        This argument is always two characters long: The first character specifi
es the
        horizontal alignment and can be either l, r or c, which stand for left, 
right
        or center. The second character specifies the vertical alignment and can
 be one
        of t, b or c, which stand for top, bottom or center respectively. If you
 omit
        this alignment argument, the default "lb" applies; however this default 
may be
        changed with poke "textalign","xx"

        Example

        open window 500,200
        clear screen
        data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
        for a=1 to 9
          read align$
          print "Alignment: ",align$
          line 50*a-15,100,50*a+15,100
          line 50*a,85,50*a,115
          text 50*a,100,"Test",align$
          inkey$
        next a

        This program draws nine crosses and writes the same text at each; howeve
r it
        goes through all possible nine alignment strings, showing their effect.

        See also

        open window, peek, poke

        ------------------------------------------------------------------------
-------

        Name

        then ? tell the long from the short form of the if-statement

        Synopsis

        if (a<b) then
          ?
        endif

        Description

        The keyword then is part of the if-statement; please see there for furth
er
        explanations. However, not every if-statement requires the keyword then:
 If the
        keyword then is present, the if-clause may extend over more than one lin
e, and
        the keyword endif is required to end it. If the keyword then is not pres
ent,
        the if-statement extends up to the end of the line, and any endif would 
be an
        error.

        Example

        if (1<2) then
          print "Hello ";
        endif

        if (2<3) print "world"
        if (2<1)
          print "!"

        This example prints Hello world. Note, that no exclamation mark (!) is p
rinted,
        which might come as a surprise and may be changed in future versions of 
yabasic
        .

        See also

        if

        ------------------------------------------------------------------------
-------

        Name

        time$ ? return a string containing the current time

        Synopsis

        print time$
        print time$()

        Description

        The time$ function returns the current time in four fields separated by 
hyphens
        '-'. The fields are:

          * The current hour in the range from 0 to 23, padded with zeroes (e.g.
 00 or
            04) to a length of two characters.

          * The number of minutes, padded with zeroes.

          * The number of seconds, padded with zeroes.

          * The number of seconds, that have elapsed since the program has been
            started. This value increases as long as your program runs and is th
erefore
            unbound and not padded with zeroes.

        At the time of writing this documentation, time$ returns 22-58-53-0. Not
e, that
        the first three of the four fields returned by time$ have a fixed width;
        therefore it is easy to extract some fields with the usual string-functi
ons
        mid$ (and others).

        Example

        print "Hello it is ",time$
        print "An empty for-loop with ten million iterations takes ";
        for a=1 to 10000000:next a
        print "Now it is ",time$
        print peek("secondsrunning")," seconds have passed."

        This program benchmarks the for-loop; however, it does not use the fourt
h field
        of the string returned by time$, because that string wraps around every 
60
        seconds; rather the peek "secondsrunning" is queried.

        See also

        date

        ------------------------------------------------------------------------
-------

        Name

        to ? this keyword appears as part of other statements

        Synopsis

        for a=1 to 100 step 2
          ?
        next a

        line x,y to a,b

        Description

        The to-keyword serves two purposes (which are not related at all):

          * within for-statements, to specify the upper bound of the loop.

          * Within any graphical command (e.g. line), that requires two points (
i.e.
            four numbers) as arguments, a comma ',' might be replaced with the k
eyword
            to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200
 in
            such commands.

        Example

        Please see the command listed under "See also" for examples.

        See also

        for, line, rectangle

        ------------------------------------------------------------------------
-------

        Name

        token() ? split a string into multiple strings

        Synopsis

        dim w$(10)
        ?
        num=token(a$,w$())
        num=token(a$,w$(),s$)

        Description

        The token-function accepts a string (containing the text to be split), a
        reference to a string-array (which will receive the resulting strings, i
.e. the
        tokens) and an optional string (with a set of characters, at which to sp
lit,
        i.e. the delimiters).

        The token-function regards its first argument as a list of tokens separa
ted by
        delimiters and it will store the list of tokens within the array-referen
ce that
        has been supplied. Note, that the array, which is passed as a reference 
(w$()
        in the synopsis), will be resized accordingly, so that you don't have to
 figure
        out the number of tokens in advance. The element at position zero (i.e. 
w$(0))
        will not be used.

        Normally (i.e. if you omit the third, the delimiter-argument) the functi
on will
        regard space or tab as delimiters for tokens; however by supplying a thi
rd
        argument, you may split at any single of the characters within this stri
ng.
        E.g. if you supply ":;" as the third argument, then colon (:) or semicol
on (;)
        will delimit tokens.

        Note, that token will never produce empty tokens, even if two or more
        separators follow in sequence. Refer to the closely related split-functi
on, if
        you do not like this behaviour. In some way, the token-function focuses 
on the
        tokens and not on the separators (other than the split-function, which f
ocuses
        on the separators).

        The second argument is a reference on a string-array, where the tokens w
ill be
        stored; this array will be expanded (or shrunk) as necessary to have roo
m for
        all tokens.

        The first argument finally contains the text, that will be split into to
kens.
        The token-function returns the number of tokens, that have been found.

        Please see the examples below for some hints on the exact behaviour of t
he
        token-function and how it differs from the split-function:

        Example

        print "This program will help you to understand, how the"
        print "token()-function exactly works and how it behaves"
        print "in certain special cases."
        print
        print "Please enter a line containing tokens separated"
        print "by either '=' or '-'"
        dim t$(10)
        do
          print
          input "Please enter a line: " l$
          num=token(l$,t$(),"=-")
          print num," Tokens: ";
          for a=1 to num
            if (t$(a)="") then
              print "(EMPTY)";
            else
              print t$(a);
            endif
            if (a<num) print ",";
          next a
          print
        loop

        This program prints the following output:

        Please enter a line: a
        1 Tokens: a

        Please enter a line:
        0 Tokens:

        Please enter a line: ab
        1 Tokens: ab

        Please enter a line: a=b
        2 Tokens: a,b

        Please enter a line: a-
        1 Tokens: a

        Please enter a line: a-=
        1 Tokens: a

        Please enter a line: =a-
        1 Tokens: a

        Please enter a line: a=-b
        2 Tokens: a,b

        Please enter a line: a--b-
        2 Tokens: a,b

        Please enter a line: -a==b-c==
        3 Tokens: a,b,c

        See also

        split

        ------------------------------------------------------------------------
-------

        Name

        triangle ? draw a triangle

        Synopsis

        open window 100,100
        triangle 100,100,50,50,100,50
        fill triangle 50,100,100,50,200,200
        clear fill triangle 20,20,10,10,200,200

        Description

        The triangle-command draws a triangle; it requires 6 parameters: The x- 
and
        y-coordinates of the three points making up the triangle. With the optio
nal
        keywords clear and fill (which may appear both and in any sequence) the
        triangle can be cleared and filled respectively.

        Example

        open window 200,200
        do
          phi=phi+0.2
          i=i+2
          color mod(i,255),mod(85+2*i,255),mod(170+3*i,255)
          dx=100*sin(phi):dy=20*cos(phi)
          fill triangle 100+20*sin(phi),100+20*cos(phi),100-20*sin(phi),100-20*c
os(phi),100-80*cos(phi),100+80*sin(phi)
          sleep 0.1
        loop

        This example draws a colored triangles until you get exhausted.

        See also

        open window, open printer, line, circle, rectangle

        ------------------------------------------------------------------------
-------

        Name

        trim$() ? remove leading and trailing spaces from its argument

        Synopsis

        a$=trim$(b$)

        Description

        The trim$-function removes all whitespace from the left and from the rig
ht end
        of a string and returns the result. Calling trim$ is equivalent to calli
ng
        rtrim$(ltrim$()).

        Example

        do
          input "Continue ? Please answer yes or no: " a$
          a$=lower$(trim$(a$))
          if (len(a$)>0 and a$=left$("no",len(a$)) exit
        loop

        This example asks for an answer (yes or no) and removes spaces with trim
$ to
        make the comparison with the string "no" more bulletproof.

        See also

        ltrim$, rtrim$

        ------------------------------------------------------------------------
-------

        Name

        true ? a constant with the value of 1

        Synopsis

        okay=true

        Description

        The constant true can be assigned to variables which will later appear i
n
        conditions (e.g. an if-statement.

        true may also be written as TRUE or even TrUe.

        Example

        input "Please enter a string of all upper letters: " a$
        if (is_upper(a$)) print "Okay"

        sub is_upper(a$)
          if (a$=upper$(a$)) return true
          return false
        end sub

        See also

        false

        U

        until ? end a repeat-loop
        upper$() ? convert a string to upper case
        using ? Specify the format for printing a number

        Name

        until ? end a repeat-loop

        Synopsis

        repeat
          ?
        until (?)

        Description

        The until-keyword ends a loop, which has been introduced by the repeat-k
eyword.
        until requires a condition in braces (or an expression, see here for det
ails)
        as an argument; the loop will continue until this condition evaluates to
 true.

        Example

        c=1
        s=1
        repeat
          l=c
          s=-(s+sig(s))
          c=c+1/s
          print c
        until(abs(l-c)<0.000001)

        This program calculates the sequence 1/1-1/2+1/3-1/4+1/5-1/6+1/7-1/8+ ? 
;
        please let me know, if you know against which value this converges.

        See also

        repeat

        ------------------------------------------------------------------------
-------

        Name

        upper$() ? convert a string to upper case

        Synopsis

        u$=upper$(a$)

        Description

        The upper$-function accepts a single string argument and converts it to 
all
        upper case.

        Example

        line input "Please enter a sentence without the letter 'e': " l$
        p=instr(upper$(l$),"E")
        if (p) then
          l$=lower$(l$)
          mid$(l$,p,1)="E"
          print "Hey, you are wrong, see here!"
          print l$
        else
          print "Thanks."
        endif

        This program asks for a sentence and marks the first (if any) occurrence
 of the
        letter 'e' by converting it to upper case (in contrast to the rest of th
e
        sentence, which is converted to lower case).

        See also

        lower$

        ------------------------------------------------------------------------
-------

        Name

        using ? Specify the format for printing a number

        Synopsis

        print a using "##.###"
        print a using("##.###",",.")

        Description

        The using-keyword may appear as part of the print-statement and specifie
s the
        format (e.g. the number of digits before and after the decimal dot), whi
ch
        should be used to print the number.

        The possible values for the format argument ("##.###" in the synopsis ab
ove)
        are described within the entry for the str$-function; especially the sec
ond
        line in the synopsis (print a using("##.###",",.")) will become clear af
ter
        referring to str$. In fact the using clause is closely related to the
        str$-function; the former can always be rewritten using the latter; i.e.
 print
        foo using bar$ is always equivalent to print str$(foo,bar$). Therefore y
ou
        should check out str$ to learn more.

        Example

        for a=1 to 10
          print sqrt(ran(10000*a)) using "#########.#####"
        next a

        This example prints a column of square roots of random number, nicely al
igned
        at the decimal dot.

        See also

        print, str$

        V

        val() ? converts a string to a number

        Name

        val() ? converts a string to a number

        Synopsis

        x=val(x$)

        Description

        The val-function checks, if the start of its string argument forms a flo
ating
        point number and then returns this number. The string therefore has to s
tart
        with digits (only whitespace in front is allowed), otherwise the val-fun
ction
        returns zero.

        Example

        input "Please enter a length, either in inches (in) or centimeters (cm) 
" l$
        if (right$(l$,2)="in") then
          l=val(l$)*2.51
        else
          l=val(l$)
        print "You have entered ",l,"cm."

        This example queries for a length and checks, if it has been specified i
n
        inches or centimeters. The length is then converted to centimeters.

        See also

        str$

        W

        wait ? pause, sleep, wait for the specified number of seconds
        wend ? end a while-loop
        while ? start a while-loop
        window origin ? move the origin of a window

        Name

        wait ? pause, sleep, wait for the specified number of seconds

        Synopsis

        wait 4

        Description

        The wait-command has many different names: You may write pause, sleep or
 wait
        interchangeably; whatever you write, yabasic will always do exactly the 
same.

        Therefore you should refer to the entry for the pause-function for furth
er
        information.

        ------------------------------------------------------------------------
-------

        Name

        wend ? end a while-loop

        Synopsis

        while(a<b)
          ?
        wend

        Description

        The wend-keyword marks the end of a while-loop. Please see the while-key
word
        for more details.

        wend can be written as end while or even end-while.

        Example

        line input "Please enter a sentence: " a$
        p=instr(a$,"e")
        while(p)
          mid$(a$,p,1)="E"
          p=instr(a$,"e")
        wend
        print a$

        This example reads a sentence and converts every occurrence of the lette
r e
        into uppercase (E).

        See also

        while (which is just the following entry).

        ------------------------------------------------------------------------
-------

        Name

        while ? start a while-loop

        Synopsis

        while(?)
          ?
        wend

        Description

        The while-keyword starts a while-loop, i.e. a loop that is executed as l
ong as
        the condition (which is specified in braces after the keyword while) eva
luates
        to true.

        Note, that the body of such a while-loop will not be executed at all, if
 the
        condition following the while-keyword is not true initially.

        If you want to leave the loop prematurely, you may use the break-stateme
nt.

        Example

        open #1,"foo"
        while(!eof(1))
          line input #1 a$
          print a$
        wend

        This program reads the file foo and prints it line by line.

        See also

        until, break, wend, do

        ------------------------------------------------------------------------
-------

        Name

        origin ? move the origin of a window

        Synopsis

        open window 200,200
        origin "cc"

        Description

        The origin-command applies to graphic windows and moves the origin of th
e
        coordinate system to one of nine point within the window. The normal pos
ition
        of the origin is in the upper left corner of the window; however in some
 cases
        this is inconvenient and moving the origin may save you from subtracting
 a
        constant offset from all of your coordinates.

        However, you may not move the origin to an arbitrary position; in horizo
ntal
        position there are only three positions: left, center and right, which a
re
        decoded by the letters l, c and r. In vertical position the allowed posi
tions
        are top, center and bottom; encoded by the letters t, c and b. Taking th
e
        letters together, you arrive at a string, which might be passed as an ar
gument
        to the command; e.g. "cc" or "rt".

        Example

        100,100

        open window 200,200
        window origin "cc"
        circle 0,0,60

        This example draws a circle, centered at the center of the window.

        See also

        open window

        X

        xor() ? compute the exclusive or

        Name

        xor() ? compute the exclusive or

        Synopsis

        x=xor(a,b)

        Description

        The xor computes the bitwise exclusive or of its two numeric arguments. 
To
        understand the result, both arguments should be viewed as binary numbers
 (i.e.
        a series of 0 and 1); a bit of the result will then be 1, if exactly one
        argument has a 1 and the other has a 0 at this position in their binary
        representation.

        Note, that both arguments are silently converted to integer values and t
hat
        negative numbers have their own binary representation and may lead to
        unexpected results when passed to and.

        Example

        print xor(7,4)

        This will print 3. This result is obvious, if you note, that the binary
        representation of 7 and 4 are 111 and 100 respectively; this will yield 
011 in
        binary representation or 2 as decimal.

        The eor-function is the same as the xor function; both are synonymous; h
owever
        they have each their own description, so you may check out the entry of 
eor for
        a slightly different view.

        See also

        and, or, eor, not

        Special characters

        # ? either a comment or a marker for a file-number
        // ? starts a comment
        @ ? synonymous to at
        : ? separate commands from each other
        ; ? suppress the implicit newline after a print-statement
        ** or ^ ? raise its first argument to the power of its second

        Name

        # ? either a comment or a marker for a file-number

        Synopsis

        # This is a comment, but the line below not !
        open #1,"foo"

        Description

        The hash ('#') has two totally unrelated uses:

          * A hash might appear in commands related with file-io. yabasic uses s
imple
            numbers to refer to open files (within input, print, peek or eof). I
n those
            commands the hash may precede the number, which species the file. Pl
ease
            see those commands for further information and examples; the rest of
 this
            entry is about the second use (as a comment).

          * As the very first character within a line, a hash introduces comment
s
            (similar to rem).

        '#' as a comment is common in most scripting languages and has a special
 use
        under Unix: If the very first line of any Unix-program begins with the
        character sequence '#!' ("she-bang", no spaces allowed), the rest of the
 line
        is taken as the program that should be used to execute the script. I.e. 
if your
        yabasic-program starts with '#!/usr/local/bin/yabasic', the program /usr
/local/
        bin/yabasic will be invoked to execute the rest of the program. As a rem
ark for
        windows-users: This mechanism ensures, that yabasic will be invoked to e
xecute
        your program; the ending of the file (e.g. .yab) will be ignored by Unix
.

        Example

        # This line is a valid comment
        print "Hello " : # But this is a syntax error, because
        print "World!" : # the hash is not the first character !

        Note, that this example will produce a syntax error and is not a valid p
rogram
        !

        See also

        input, print, peek or eof, //, rem

        ------------------------------------------------------------------------
-------

        Name

        // ? starts a comment

        Synopsis

        //  This is a comment !

        Description

        The double-slash ('//') is (besides REM and '#') the third way to start 
a
        comment. '//' is the latest and greatest in the field of commenting and 
allows
        yabasic to catch up with such cool languages like C++ and Java.

        Example

        // Another comment.
        print "Hello world !" // Another comment

        Unlike the example given for '#' this example is syntactically correct a
nd will
        not produce an error.

        See also

        #, rem

        ------------------------------------------------------------------------
-------

        Name

        @ ? synonymous to at

        Synopsis

        clear screen
        ?
        print @(a,b)

        Description

        As '@' is simply a synonym for at, please see at for further information
.

        See also

        at

        ------------------------------------------------------------------------
-------

        Name

        : ? separate commands from each other

        Synopsis

        print "Hello ":print "World"

        Description

        The colon (':') separates multiple commands on a single line.

        The colon and the newline-character have mostly the same effect, only th
at the
        latter, well, starts a new line too. The only other difference is their 
effect
        within the (so-called) short if, which is an if-statement without the ke
yword
        then. Please see the entry for if for more details.

        Example

        if (a<10) print "Hello ":print "World !"

        This example demonstrates the difference between colon and newline as de
scribed
        above.

        See also

        if

        ------------------------------------------------------------------------
-------

        Name

        ; ? suppress the implicit newline after a print-statement

        Synopsis

        print "foo",bar;

        Description

        The semicolon (';') may only appear at the last position within a print
        -statement. It suppresses the implicit newline, which yabasic normally a
dds
        after each print-statement.

        Put another way: Normally the output of each print-statement appears on 
a line
        by itself. If you rather want the output of many print-statements to app
ear on
        a single line, you should end the print-statement with a semicolon.

        Example

        print "Hello ";:print "World !"

        This example prints Hello World ! in a single line.

        See also

        print

        ------------------------------------------------------------------------
-------

        Name

        ** or ^ ? raise its first argument to the power of its second

        Synopsis

        print 2**b
        print 3^4

        Description

        ** (or ^, which is an exact synonym), is the arithmetic operator of
        exponentiation; it requires one number to its left and a second one to i
ts
        right; ** then raises the first argument to the power of the second and 
returns
        the result. The result will only be computed if it yields a real number 
(as
        opposed to a complex number); this means, that the power can not be comp
uted,
        if the first argument is negative and the second one is fractional. On t
he
        other hand, the second argument can be fractional, if the first one ist
        positive; this means, that ** may be used to compute arbitrary roots: e.
g.
        x**0.5 computes the square root of x.

        Example

        print 2**0.5

        See also

        sqrt

        Reserved Words

        Here is a list of all reserved words in yabasic. Please make sure, that 
you do
        not try to use one of them as the name of a variable or subroutine. Or, 
the
        other way around: If you get some mysterious error from yabasic and you 
just
        can't figure out why, then you might be using one of the reserved words 
below,
        without knowing.

        Anyway, here is the list:

        ABS       ACOS          AND      ARRAYDIM   ARRAYDIMENSION
        ARRAYSIZE AS            ASC      ASIN       AT
        ATAN      BEEP          BELL     BIN$       BIND
        BITBLIT   BITBLIT$      BITBLT   BITBLT$    BOX
        BREAK     CASE          CHR$     CIRCLE     CLEAR
        CLOSE     COLOR         COLOUR   COMPILE    CONTINUE
        COS       CURVE         DATA     DATE$      DEC
        DEFAULT   DIM           DO       DOT        ELSE
        ELSEIF    ELSIF         END      ENDIF      EOF
        EOR       ERROR         EXECUTE  EXECUTE$   EXIT
        EXP       EXPORT        FI       FILL       FILLED
        FOR       FRAC          GETBIT$  GETSCREEN$ GLOB
        GOSUB     GOTO          HEX$     IF         INKEY$
        INPUT     INSTR         INT      INTERRUPT  LABEL
        LEFT$     LEN           LET      LINE       LOCAL
        LOG       LOOP          LOWER$   LTRIM$     MAX
        MID$      MIN           MOD      MOUSEB     MOUSEBUTTON
        MOUSEMOD  MOUSEMODIFIER MOUSEX   MOUSEY     NEW
        NEXT      NOT           NUMPARAM ON         OPEN
        OR        ORIGIN        PAUSE    PEEK       PEEK$
        POKE      PRINT         PRINTER  PUTBIT     PUTSCREEN
        RAN       READ          READING  RECT       RECTANGLE
        REDIM     REPEAT        RESTORE  RETURN     REVERSE
        RIGHT$    RINSTR        RTRIM$   SCREEN     SEEK
        SIG       SIN           SLEEP    SPLIT      SPLIT$
        SQR       SQRT          STATIC   STEP       STR$
        SUB       SUBROUTINE    SWITCH   SYSTEM     SYSTEM$
        TAN       TELL          TEXT     THEN       TIME$
        TO        TOKEN         TOKEN$   TRIANGLE   TRIM$
        UNTIL     UPPER$        USING    VAL        WAIT
        WEND      WHILE         WINDOW   WRITING    XOR

        Please see here for explanations on how to use these words in yabasic.

        Chapter 8. Some general concepts and terms

        Logical shortcuts
        Conditions and expressions
        References on arrays
        Specifying Filenames under Windows
        Escape-sequences
        Creating a standalone program from your yabasic-program

        This chapter presents some general concepts and terms, which deserve a
        description on their own, but are not associated with a single command o
r
        function in yabasic. Most of these topics do not lend themselves to be r
ead
        alone, rather they might be read (or skimmed) as background material if 
an
        entry from the alphabetical list of commands refers to them.

        Logical shortcuts

        Logical shortcuts are no special language construct and there is no keyw
ord for
        them; they are just a way to evaluate logical expressions. Logical expre
ssions
        (i.e. a series of conditions or comparisons joined by and or or) are onl
y
        evaluated until the final result of the expression can be determined. An
        example:

        if (a<>0 and b/a>2) print "b is at least twice as big as a"

        The logical expression a<>0 and b/a>2 consists of two comparisons, both 
of
        which must be true, if the print statement should be executed. Now, if t
he
        first comparison (a<>0) is false, the whole logical expression can never
 be
        true and the second comparison (b/a>2) need not be evaluated.

        This is exactly, how yabasic behaves: The evaluation of a composed logic
al
        expressions is terminated immediately, as soon as the final result can b
e
        deduced from the already evaluated parts.

        In practice, this has the following consequences:

          * If two or more comparisons are joined with and and one comparison re
sults
            in false, the logical expression is evaluated no further and the ove
rall
            result is false.

          * If two or more comparisons are joined with or and one comparison res
ults in
            true, the logical expression is evaluated no further and the result 
is
            true.

        ?Nice, but whats this good for ??, I hear you say. Well, just have anoth
er look
        at the example, especially the second comparison (b/a>2); dividing b by 
a is
        potentially hazardous: If a equals zero, the expression will cause an er
ror and
        your program will terminate. To avoid this, the first part of the compar
ison (a
        <>0) checks, if the second one can be evaluated without risk. This pre-c
hecking
        is the most common usage and primary motivation for logical shortcuts (a
nd the
        reason why most programming languages implement them).

        Conditions and expressions

        Well, bottomline there is no difference or distinction between condition
s and
        expressions, at least as yabasic is concerned. So you may assign the res
ult of
        comparisons to variables or use an arithmetic expression or a simple var
iable
        within a condition (e.g. within an if-statement). So the constructs show
n in
        the example below are all totally valid:

        input "Please enter a number between 1 and 10: " a

        rem   Assigning the result of a comparison to a variable
        okay=a>=1 and a<=10

        rem   Use a variable within an if-statement
        if (not okay) error "Wrong, wrong !"

        So conditions and expressions are really the same thing (at least as lon
g as
        yabasic is concerned). Therefore the terms conditions and expression can
 really
        be used interchangeably, at least in theory. In reality the term conditi
on is
        used in connection with if or while whereas the term expression tends to
 be
        used more often within arithmetic context.

        References on arrays

        References on arrays are the only way to refer to an array as a whole an
d to
        pass it to subroutines or functions like arraydim or arraysize. Whereas 
(for
        example) a(2) designates the second element of the array a, a() (with em
pty
        braces) refers to the array a itself. a() is called an array reference.

        If you pass an array reference to one of your own subroutines, you need 
to be
        aware, that the subroutine will be able to modify the array you have pas
sed in.
        So passing an array reference does not create a copy of the array; this 
has
        some interesting consequences:

          * Speed and space: Creating a copy of an array would be a time (and re
source)
            consuming operation; passing just a reference is cheap and fast.

          * Returning many values: A subroutine, that wants to give back more th
an one
            value, may require an array reference among its arguments and then s
tore
            its many return values within this array. This is the only way to re
turn
            more than one value from a subroutine.

        Specifying Filenames under Windows

        As you probably know, windows uses the character '\' to separate the
        directories within a pathname; an example would be C:\yabasic\yabasic.ex
e (the
        usual location of the yabasic executable). However, the very same charac
ter '\'
        is used to construct escape sequences, not only in yabasic but in most o
ther
        programming languages.

        Therefore the string "C:\t.dat" does not specify the file t.dat within t
he
        directory C:; this is because the sequence '\t' is translated into the
        tab-character. To specify this filename, you need to use the string "C:\
\t.dat"
        (note the double slash '\\').

        Escape-sequences

        Escape-sequences are the preferred way of specifying 'special' character
s. They
        are introduced by the '\'-character and followed by one of a few regular
        letters, e.g. '\n' or '\r' (see the table below).

        Escape-sequences may occur within any string at any position; they are r
eplaced
        at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the
        string, with their corresponding special character. As a consequence of 
this
        len("\a") returns 1, because yabasic replaces "\a" with the matching spe
cial
        character just before the program executes.

        Table 8.1. Escape sequences

        +--------------------------------------------+
        |Escape Sequence| Matching special character |
        |---------------+----------------------------|
        |\n             |newline                     |
        |---------------+----------------------------|
        |\t             |tabulator                   |
        |---------------+----------------------------|
        |\v             |vertical tabulator          |
        |---------------+----------------------------|
        |\b             |backspace                   |
        |---------------+----------------------------|
        |\r             |carriage return             |
        |---------------+----------------------------|
        |\f             |formfeed                    |
        |---------------+----------------------------|
        |\a             |alert (i.e. a beeping sound)|
        |---------------+----------------------------|
        |\\             |backslash                   |
        |---------------+----------------------------|
        |\'             |single quote                |
        |---------------+----------------------------|
        |\"             |double quote                |
        |---------------+----------------------------|
        |\xHEX          |chr$(HEX) (see below)       |
        +--------------------------------------------+

        Note, that an escape sequences of the form \xHEX allows one to encode ar
bitrary
        characters as long as you know their position (as a hex-number) within t
he
        ascii-charset: For example \x012 is transformed into the character chr$(
18) (or
        chr$(dec("12",16)). Note that \x requires a hexa-decimal number (and the
        hexa-decimal string "12" corresponds to the decimal number 18).

        Creating a standalone program from your yabasic-program

        Creating a standalone-program from the command line
        Creating a standalone-program from within your program
        Downsides of creating a standalone program
        See also

        Note

        The bind-feature, which is described below, is at an experimental stage 
right
        now. It works (at least for me !) under Windows and Linux, but I cannot 
even
        promise it for other variants of Unix. However, if it does not work for 
your
        Unix, I will at least try to make it work, if you give me sufficient
        information of your system.

        Sometimes you may want to give one of your yabasic-programs to other peo
ple.
        However, what if those other people do not have yabasic installed ? In t
hat
        case you may create a standalone-program from your yabasic-program, i.e.
 an
        executable, that may be executed on its own, standalone, even (and espec
ially
        !) on computers, that do not have yabasic installed. Having created a
        standalone program, you may pass it around like any other program (e.g. 
one
        written in C) and you can be sure that your program will execute right a
way.

        Such a standalone-program is simply created by copying the full yabasic
        -interpreter and your yabasic-program (plus all the libraries it does im
port)
        together into a single, new program, whose name might be chosen at will 
(under
        windows of course it should have the ending .exe). If you decide to crea
te a
        standalone-program, there are three bits in yabasic, that you may use:

          * The bind-command, which does the actual job of creating the standalo
ne
            program from the yabasic-interpreter and your program.

          * The command-line Option --bind (see options), which does the same fr
om the
            command-line.

          * The special peek("isbound"), which may be used to check, if the yaba
sic
            -program containing this peek is bound to the interpreter as part of
 a
            standalone program.

        With these bits you know enough to create a standalone-program. Actually
 there
        are two ways to do this: on the command line and from within your progra
m.

        Creating a standalone-program from the command line

        Let's say you have the following very simple program within the file foo
.yab:

        print "Hello World !"

        Normally you would start this yabasic-program by typing yabasic foo.yab 
and as
        a result the string Hello World ! would appear on your screen. However, 
to
        create a standalone-program from foo.yab you would type:

        yabasic -bind foo.exe foo.yab

        This command does not execute your program foo.yab but rather create a
        standalone-program foo.exe. Note: under Unix you would probably name the
        standalone program foo or such, omitting the windows-specific ending .ex
e.

        Yabasic will confirm by printing something like: ---Info: Successfully b
ound
        'yabasic' and 'foo.yab' into 'foo.exe'.

        After that you will find a program foo.exe (which must be made executabl
e with
        the chmod-command under Unix first). Now, executing this program foo.exe
 (or
        foo under Unix) will produce the output Hello World !.

        This newly created program foo.exe might be passed around to anyone, eve
n if he
        does not have yabasic installed.

        Creating a standalone-program from within your program

        It is possible to write a yabasic-program, that binds itself to the yaba
sic
        -interpreter. Here is an example:

        if (!peek("isbound")) then
          bind "foo"
          print "Successfully created the standalone executable 'foo' !"
          exit
        endif

        print "Hello World !"

        If you run this program (which may be saved in the file foo.yab) via yab
asic
        foo.yab, the peek("isbound") in the first line will check, if the progra
m is
        already part of a standalone-program. If not (i.e. if the yabasic-interp
reter
        and the yabasic-program are separate files) the bind-command will create
 a
        standalone program foo containing both. As a result you would see the ou
tput
        Successfully created the standalone executable 'foo' !. Note: Under Wind
ows you
        would probably choose the filename foo.exe.

        Now, if you run this standalone executable foo (or foo.exe), the very sa
me
        yabasic-program that is shown above will be executed again. However, thi
s time
        the peek("isbound") will return TRUE and therefore the condition of the
        if-statement is false and the three lines after then are not executed. R
ather
        the last print-statement will run, and you will see the output Hello Wor
ld !.

        That way a yabasic-program may turn itself into a standalone-program.

        Downsides of creating a standalone program

        Now, before you go out and turn all your yabasic-programs into standalon
e
        programs, please take a second to consider the downsides of doing so:

          * The new standalone program will be at least as big as the interprete
r
            itself, so you need to pass a few hundred kilobytes around, just to 
save
            people from having to install yabasic themselves.

          * There is no easy way to extract your yabasic-program from within the
            standalone program: If you ever want to change it, you need to have 
it
            around separately.

          * If a new version of yabasic becomes available, again you need to rec
reate
            all of your standalone programs to take advantage of bugfixes and
            improvements.

        So, being able to create a standalone program is certainly a good thing,
 but
        certainly not a silver bullet.

        See also

        The bind-command, the peek-function and the command line options.

        Chapter 9. A few example programs

        A very simple program
        The demo of yabasic

        A very simple program

        The program below is a very simple program:

        repeat
          input "Please enter the first number, to add " a
          input "Please enter the second number, to add " b
          print a+b
        until(a=0 and b=0)

        This program requests two numbers, which it than adds. The process is re
peated
        until you enter zero (or nothing) twice.

        The demo of yabasic

        The listing below is the demo of yabasic. Note, that parts of this demo 
have
        been written before some of the more advanced features (e.g subroutines)
 of
        yabasic have been implemented. So please do not take this as a particula
r good
        example of yabasic-code.

        //
        //      This program demos yabasic
        //

        //      Check, if screen is large enough
        clear screen
        sw=peek("screenwidth"):sh=peek("screenheight")
        if (sw<78 or sh<24) then
          print
          print "  Sorry, but your screen is to small to run this demo !"
          print
          end
        endif
        sw=78:sh=24

        //  Initialize everything
        restore mmdata
        read mmnum:dim mmtext$(mmnum)
        for a=1 to mmnum:read mmtext$(a):next a

        //  Main loop selection of demo
        ysel=1
        label mainloop
        clear screen
        print colour("cyan","magenta") at(7,2) "################################
"
        print colour("cyan","magenta") at(7,3) "################################
"
        print colour("cyan","magenta") at(7,4) "################################
"
        print colour("yellow","blue") at(8,3) " This is the demo for yabasic "
        yoff=7
        for a=1 to mmnum
          if (a=mmnum) then ydisp=1:else ydisp=0:fi
          if (a=ysel) then
            print colour("blue","green") at(5,yoff+ydisp+a) mmtext$(a);
          else
            print at(5,yoff+ydisp+a) mmtext$(a);
          endif
        next a
        print at(3,sh-3) "Move selection with CURSOR KEYS (or u and d),"
        print at(3,sh-2) "Press RETURN or SPACE to choose, ESC to quit."

        do    // loop for keys pressed
          rev=1
          do    // loop for blinking
            k$=inkey$(0.4)
            if (k$="") then
              if (ysel=mmnum) then
                if (rev=1) then
                  print colour("blue","green") at(5,yoff+mmnum+1) mmtext$(mmnum)
;
                  rev=0
                else
                  print colour("yellow","red") at(5,yoff+mmnum+1) mmtext$(mmnum)
;
                  rev=1
                endif
              endif
            else    // key has been pressed, leave loop
              break
            endif
          loop    // loop for blinking

          yalt=ysel
          if (k$="up" or k$="u") then
            if (ysel=1) then ysel=mmnum else ysel=ysel-1 fi
            redraw():heal():continue
          fi
          if (k$="down" or k$="d") then
            if (ysel=mmnum) then ysel=1 else ysel=ysel+1 fi
            redraw():heal():continue
          fi
          if (k$=" " or k$="enter" or k$="right") then
            on ysel gosub overview,bitmap,tetraeder,endit
            goto mainloop
          fi
          if (k$="esc") then
            endit()
          fi
          beep
          print at(3,sh-5) "Invalid key: ",k$,"         "
        loop    // loop for keys pressed

        //  redraw line
        sub redraw()
          if (yalt=mmnum) then ydisp=1:else ydisp=0:fi
          print at(5,yoff+yalt+ydisp) mmtext$(yalt);
          if (ysel=mmnum) then ydisp=1:else ydisp=0:fi
          print colour("blue","green") at(5,yoff+ysel+ydisp) mmtext$(ysel);
          return
        end sub

        //  erase a line
        sub heal()
          print at(3,sh-5) "                                                    
   "
          return
        end sub

        //  Go here to exit
        label endit
          print at(3,sh-8) "Hope you liked it ...\n   ";
          exit
        return

        //  Present a short overview
        label overview
          clear screen
          print
          print "  Yabasic is a quite traditional basic: It comes with"
          print "  print, input, for-next-loops, goto, gosub, while and"
          print "  repeat. It has user defined procedures and libraries,"
          print "  however, it is not object oriented.\n"
          print "  Yabasic makes it easy to open a window, draw lines"
          print "  and print the resulting picture.\n"
          print "  Yabasic programs are interpreted and run under Unix"
          print "  and Windows. The Yabasic interpreter (around 200K)"
          print "  and any Yabasic program can be glued together to"
          print "  form a standalone executable.\n"
          print "  Yabasic is free software, i.e. subject to the"
          print "  MIT License.\n"
          print "\n\n\n  While you read this, I am calculating prime numbers,\n"
          print "  Press any key to return to main menu ..."
          can=1
          print at(6,17) "This is a prime number: "
          label nextcan
          can=can+2
          for i=2 to sqrt(can):if (frac(can/i)=0) then goto notprime:fi:next i
          print at(32,17) can;
          label notprime
          if (lower$(inkey$(0))<>"") then
            print at(10,sh) "Wrapping around once ...";
            for x=1 to sw
              a$=getscreen$(0,0,1,sh-2)
              b$=getscreen$(1,0,sw-1,sh-2)
              putscreen b$,0,0
              putscreen a$,sw-1,0
            next x
            sleep 2
            return
          fi
        goto nextcan

        //  Show some animated bitmaps
        label bitmap
          clear screen
          print
          print "Yabasic offers some commands for drawing simple graphics."
          print reverse at(5,12) " Press any key to return to main menu ... "

          n=20
          open window 400,400

          for b=20 to 0 step -1
            color 255-b*12,0,b*12
            fill circle 200,200,b
          next b
          c$=getbit$(179,179,221,221)
          for a=1 to 2000
            color ran(255),ran(255),ran(255)
            x=ran(500)-100:y=ran(500)-100
            fill rectangle ran(500)-100,ran(500)-100,ran(500)-100,ran(500)-100
          next a

          x=200:y=200:phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
          o$=""
          count=0
          label pong
            count=count+1
            if (o$<>"") putbit o$,xo-2,yo-2
            if (count>1000) then
              phi=ran(2*pi):dx=2*sin(phi):dy=2*cos(phi)
              sleep 2
              count=0
            endif
            xo=x:yo=y
            x=x+dx:y=y+dy
            o$=getbit$(x-2,y-2,x+46,y+46)
            putbit c$,x,y,"t"
            if (x<0 or x>360) dx=-dx
            if (y<0 or y>360) dy=-dy
            if (inkey$(0)<>"") then
              close window
              return
            endif
          goto pong
        return

        label tetraeder

        open window 400,400
        clear window
        clear screen
        print reverse at(5,12) " Press any key to return to main menu ... "

        dim opoints(4,3)
        restore points
        for n=1 to 4:for p=1 to 3:read opoints(n,p):next p:next n

        dim triangles(4,3)
        restore triangles
        for n=1 to 4:for p=1 to 3:read triangles(n,p):next p:next n

        phi=0:dphi=0.1:psi=0:dpsi=0.05
        dim points(4,3)

        r=60:g=20
        dr=0.5:dg=1.2:db=3
        label main

          phi=phi+dphi
          psi=psi+dpsi
          for n=1 to 4
            points(n,1)=opoints(n,1)*cos(phi)-opoints(n,2)*sin(phi)
            points(n,2)=opoints(n,2)*cos(phi)+opoints(n,1)*sin(phi)
            p2=          points(n,2)*cos(psi)-opoints(n,3)*sin(psi)
            points(n,3)=opoints(n,3)*cos(psi)+ points(n,2)*sin(psi)
            points(n,2)=p2
          next n

          r=r+dr:if (r<0 or r>60) dr=-dr
          g=g+dg:if (g<0 or g>60) dg=-dg
          b=b+db:if (b<0 or b>60) db=-db
          dm=dm+0.01
          m=120-80*sin(dm)
          for n=1 to 4
            p1=triangles(n,1)
            p2=triangles(n,2)
            p3=triangles(n,3)
            n1=points(p1,1)+points(p2,1)+points(p3,1)
            n2=points(p1,2)+points(p2,2)+points(p3,2)
            n3=points(p1,3)+points(p2,3)+points(p3,3)
            if (n3>0) then
              sp=n1*0.5-n2*0.7-n3*0.6
              color 60+r+30*sp,60+g+30*sp,60+b+30*sp
              fill triangle 200+m*points(p1,1),200+m*points(p1,2),200+m*points(p
2,1),200+m*points(p2,2),200+m*points(p3,1),200+m*points(p3,2)
            endif
          next n
          if (inkey$(0.1)<>"") close window:return
          clear window
        goto main

        label points
        data  -1,-1,+1,  +1,-1,-1,  +1,+1,+1,  -1,+1,-1
        label triangles
        data  1,2,4,  2,3,4,  1,3,4,  1,2,3

        //  Data section ...
        label mmdata
        //  Data for main menu: Number and text of entries in main menu
        data 4
        data "   Yabasic in a nutshell   "
        data "   Some graphics           "
        data "   A rotating Tetraeder    "
        data "   Exit this demo          "

        Chapter 10. The Copyright of yabasic

        yabasic may be copied under the terms of the MIT License, which is distr
ibuted
        with yabasic in the file LICENSE.

        The MIT License grants extensive rights as long as you keep the copyrigh
t
        notice present in most files untouched. Here is a list of things that ar
e
        possible under the terms of the MIT License:

          * Put yabasic on your own homepage or CD and even charge for the servi
ce of
            distributing yabasic.

          * Write your own yabasic-programs, pack your program and yabasic into 
a
            package and sell the whole thing.

          * Modify yabasic and add or remove features, sell the modified version
            without adding the sources.

AUTHOR
       Marc Ihm, with the input and suggestions from many others.

SEE ALSO
       yabasic.htm - for the hyperlinked version of the text that is presented
       above.

       www.yabasic.de - for further information on yabasic.

BUGS
       Still some.

```
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