While loop - wikipedia While loop This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( October 2016 ) While loop flow diagram Loop constructs Do while loop While loop For loop Foreach loop Infinite loop Control flow In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement. Contents 1 Overview 2 Equivalent constructs 3 Demonstrating while loops 3.1 ActionScript 3 3.2 Ada 3.3 Microsoft Small Basic 3.4 Visual Basic 3.5 Bourne ( Unix ) shell 3.6 Fortran 3.7 Java, C#, D 3.8 JavaScript 3.9 Lua 3.10 MATLAB 3.11 Mathematica 3.12 Oberon, Oberon - 2 ( programming language ), Oberon - 07, or Component Pascal 3.13 Maya Embedded Language 3.14 Pascal 3.15 Perl 3.16 PHP 3.17 PL / I 3.18 Python 3.19 Racket 3.20 Ruby 3.21 Smalltalk 3.22 Swift 3.23 Tcl 3.24 VEX 3.25 Windows PowerShell 3.26 While programming language 4 See also 5 References Overview The while construct consists of a block of code and a condition / expression. The condition / expression is evaluated, and if the condition / expression is true, the code within the block is executed. This repeats until the condition / expression becomes false. Because the while loop checks the condition / expression before the block is executed, the control structure is often also known as a pre-test loop. Compare this with the do while loop, which tests the condition / expression after the loop has executed. For example, in the C programming language ( as well as Java, C#, Objective - C, and C++, which use the same syntax in this case ), the code fragment int x = 0 ; while ( x < 5 ) ( printf ( `` x = % d \n '', x ) ; x + + ; ) first checks whether x is less than 5, which it is, so then the ( loop body ) is entered, where the printf function is run and x is incremented by 1. After completing all the statements in the loop body, the condition, ( x < 5 ), is checked again, and the loop is executed again, this process repeating until the variable x has the value 5. Note that it is possible, and in some cases desirable, for the condition to always evaluate to true, creating an infinite loop. When such a loop is created intentionally, there is usually another control structure ( such as a break statement ) that controls termination of the loop. For example : while ( true ) ( / / do complicated stuff if ( someCondition ) break ; / / more stuff ) Equivalent constructs In the C programming language, while ( condition ) ( statements ; ) is equivalent to if ( condition ) ( do ( statements ; ) while ( condition ) ; ) or while ( true ) ( if ( ! condition ) break ; statements ; ) or goto TEST ; LOOPSTART : statements ; TEST : if ( condition ) goto LOOPSTART ; or TEST : if ( ! condition ) goto LOOPEND ; statements goto TEST ; LOOPEND : Those last two are not recommended because the use of `` goto '' statements makes it hard for a programmer to understand the flow of control, and is generally regarded as a last resort. Also, in C and its descendants, a while loop is a for loop with no initialization or counting expressions, i.e., for ( ; condition ; ) ( statements ; ) Demonstrating while loops These while loops will calculate the factorial of the number 5 : ActionScript 3 var counter : int = 5 ; var factorial : int = 1 ; while ( counter > 1 ) ( factorial * = counter ; counter -- ; ) Printf ( `` Factorial = % d '', factorial ) ; Ada The Wikibook Ada_Programming has a page on the topic of : Control with Ada. Integer_Text_IO ; procedure Factorial is Counter : Integer : = 5 ; Factorial : Integer : = 1 ; begin while Counter > 0 loop Factorial : = Factorial * Counter ; Counter : = Counter - 1 ; end loop ; Ada. Integer_Text_IO. Put ( Factorial ) ; end Factorial ; Microsoft Small Basic counter = 5 ' Counter = 5 factorial = 1 ' initial value of variable `` factorial '' While counter > 0 factorial = factorial * counter counter = counter - 1 TextWindow. WriteLine ( counter ) EndWhile Visual Basic Dim counter As Integer = 5 ' init variable and set value Dim factorial As Integer = 1 ' initialize factorial variable Do While counter > 0 factorial = factorial * counter counter = counter - 1 Loop ' program goes here, until counter = 0 ' Debug. Print factorial ' Console. WriteLine ( factorial ) in Visual Basic. NET Bourne ( Unix ) shell counter = 5 factorial = 1 while ( $ counter - gt 0 ) ; do factorial = $ ( ( factorial * counter ) ) counter = $ ( ( counter - 1 ) ) done echo $ factorial include < stdio. h > int main ( ) ( int i = 10 ; while ( i = = 10 ) ; ( printf ( `` % d '', i ) ; i++ ; ) ) Fortran program FactorialProg integer : : counter = 5 integer : : factorial = 1 do while ( counter > 0 ) factorial = factorial * counter counter = counter - 1 end do print *, factorial end program FactorialProg Java, C#, d The code for the loop is the same for Java, C# and D: int counter = 5 ; long factorial = 1 ; while ( counter > 1 ) ( factorial * = counter -- ; ) For Java the result is printed as follows : System. out. println ( factorial ) ; The same in C# System. Console. WriteLine ( factorial ) ; And finally in D writefln ( factorial ) ; JavaScript var counter = 5 ; var factorial = 1 ; while ( counter > 1 ) ( factorial * = counter -- ; ) document. write ( factorial ) ; Lua counter = 5 factorial = 1 while counter > 0 do factorial = factorial * counter counter = counter - 1 end print ( factorial ) MATLAB counter = 5 ; factorial = 1 ; while ( counter > 0 ) factorial = factorial * counter ; % Multiply counter = counter - 1 ; % Decrement end factorial Mathematica Block ( ( counter = 5, factorial = 1 ), ( * localize counter and factorial * ) While ( counter > 0, ( * While loop * ) factorial * = counter ; ( * Multiply * ) counter -- ; ( * Decrement * ) ) ; factorial ) Oberon, oberon - 2 ( programming language ), oberon - 07, or component Pascal MODULE Factorial ; IMPORT Out ; VAR Counter, Factorial : INTEGER ; BEGIN Counter : = 5 ; Factorial : = 1 ; WHILE Counter > 0 DO Factorial : = Factorial * Counter ; DEC ( Counter ) END ; Out.Int ( Factorial, 0 ) END Factorial. Maya Embedded Language int $ counter = 5 ; int $ factorial = 1 ; int $ multiplication ; while ( $ counter > 0 ) ( $ multiplication = ( $ factorial * $ counter ) ; $ counter - = 1 ; print ( `` Counter is : '' + $ counter + ``, multiplication is : '' + $ multiplication + `` \n '' ) ; ) Pascal program Factorial1 ; var Counter, Factorial : integer ; begin Counter : = 5 ; Factorial : = 1 ; while Counter > 0 do begin Factorial : = Factorial * Counter ; Counter : = Counter - 1 end ; WriteLn ( Factorial ) end. Perl my $ counter = 5 ; my $ factorial = 1 ; while ( $ counter > 0 ) ( $ factorial * = $ counter -- ; # Multiply, then decrement ) print $ factorial ; While loops are frequently used for reading data line by line ( as defined by the $ / line separator ) from open filehandles : open IN, `` < test. txt '' ; while ( < IN > ) ( print ; ) close IN ; PHP $ counter = 5 ; $ factorial = 1 ; while ( $ counter > 0 ) ( $ factorial * = $ counter ; / / Multiply first. $ counter -- ; / / then decrement. ) print $ factorial ; PL / I declare counter fixed initial ( 5 ) ; declare factorial fixed initial ( 1 ) ; do while ( counter > 0 ) factorial = factorial * counter ; counter = counter - 1 ; end ; Python counter = 5 # Set the value to 5 factorial = 1 # Set the value to 1 while counter > 0 : # While counter ( 5 ) is greater than 0 factorial * = counter # Set new value of factorial to # factorial x counter. counter - = 1 # Set the new value of counter to # counter - 1. print ( factorial ) # Print the value of factorial. Non-terminating while loop : while True : print ( `` Help ! I 'm stuck in a loop ! '' ) Racket In Racket, as in other Scheme implementations, a named - let is a popular way to implement loops : # lang racket ( define counter 5 ) ( define factorial 1 ) ( let loop ( ) ( when ( > counter 0 ) ( set ! factorial ( * factorial counter ) ) ( set ! counter ( sub1 counter ) ) ( loop ) ) ) ( displayln factorial ) Using a macro system, implementing a while loop is a trivial exercise ( commonly used to introduce macros ) : # lang racket ( define - syntax - rule ( while test body... ) ; implements a while loop ( let loop ( ) ( when test body... ( loop ) ) ) ) ( define counter 5 ) ( define factorial 1 ) ( while ( > counter 0 ) ( set ! factorial ( * factorial counter ) ) ( set ! counter ( sub1 counter ) ) ) ( displayln factorial ) But note that an imperative programming style is often discouraged in Racket ( as in Scheme ). Ruby # Calculate the factorial of 5 i = 1 factorial = 1 while i < 5 factorial * = i i + = 1 end puts factorial Smalltalk Contrary to other languages, in Smalltalk a while loop is not a language construct but defined in the class BlockClosure as a method with one parameter, the body as a closure, using self as the condition. Smalltalk also has a corresponding whileFalse : method. count factorial count : = 5. factorial : = 1. ( count > 0 ) whileTrue : ( factorial : = factorial * count. count : = count - 1 ). Transcript show : factorial Swift var counter = 5 / / Set the value to 5 var factorial = 1 / / Set the value to 1 while counter > 0 ( / / While counter ( 5 ) is greater than 0 factorial * = counter / / Set new value of factorial to factorial x counter. counter - = 1 / / Set the new value of counter to counter - 1. ) print ( factorial ) / / Print the value of factorial. Tcl set counter 5 set factorial 1 while ( $ counter > 0 ) ( set factorial ( expr $ factorial * $ counter ) incr counter - 1 ) puts $ factorial VEX int counter = 5 ; int factorial = 1 ; while ( counter > 1 ) factorial * = counter -- ; printf ( `` % d '', factorial ) ; Windows PowerShell $ number = 5 $ counter = $ number $ factorial = 1 while ( $ counter ) ( $ factorial * = $ counter -- ) $ factorial While programming language The While programming language is a simple programming language constructed from assignments, sequential composition, conditionals and while statements, used in the theoretical analysis of imperative programming language semantics. C : = 5 ; F : = 1 ; while ( C > 1 ) do F : = F * C ; C : = C - 1 ; See also Do while loop For loop Foreach LOOP ( programming language ) -- a programming language with the property that the functions it can compute are exactly the primitive recursive functions References ^ Jump up to : `` The while and do - while Statements ( The Java TM Tutorials > Learning the Java Language > Language Basics ) ''. Dosc.oracle.com. Retrieved 2016 - 10 - 21. Jump up ^ `` while ( C# reference ) ''. Msdn.microsoft.com. Retrieved 2016 - 10 - 21. Jump up ^ `` Chapter 3 : The While programming language '' ( PDF ). Profs.sci.univr.it. Retrieved 2016 - 10 - 21. Jump up ^ Flemming Nielson ; Hanne R. Nielson ; Chris Hankin ( 1999 ). Principles of Program Analysis. Springer. ISBN 978 - 3 - 540 - 65410 - 0. Retrieved 29 May 2013. Jump up ^ Illingworth, Valerie ( 11 December 1997 ). Dictionary of Computing. Oxford Paperback Reference ( 4th ed. ). Oxford University Press. ISBN 9780192800466. Retrieved from `` https://en.wikipedia.org/w/index.php?title=While_loop&oldid=821816402 '' Categories : Control flow Articles with example Fortran code Articles with example Racket code Articles with example Smalltalk code Hidden categories : Pages with syntax highlighting errors Articles needing additional references from October 2016 All articles needing additional references All articles with links needing disambiguation Articles with links needing disambiguation from April 2017 Articles with example Ada code Articles with example C code Articles with example Pascal code Articles with example Perl code Articles with example Python code Talk Contents About Wikipedia Català Čeština Dansk Ελληνικά Español Euskara Français 한국어 Hrvatski 日本 語 Português Српски / srpski Suomi Svenska Türkçe 中文 Edit links This page was last edited on 22 January 2018, at 20 : 20. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. 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Question: the while loop is this type of loop
Answer: pre-test loop