# TI-Basic Z80 Programming/Loops

It is important while writing programs to save space due to the calculator's limited memory. To help this, loops can be used which can repeat a section of code a number of times. TI-Basic offers a few types of loops: While, For, and Repeat.

## While

The While (PRGM CTL 5) loop executes a block of commands between the While and End commands as long as the specified condition is true. The condition is tested at the beginning of the loop (when the End command is encountered), so if the condition is initially false, the block of commands will never execute.

### Syntax

* Where condition is any statement resulting in a true/false/zero/non-zero result
** If condition returns true or non-zero, statement continues to execute
** If condition returns false or zero, statement will not execute and will skip to after the End

### Examples

The following example demonstrates a very basic While Loop that will display X until Y equals 0:
    While Y≠0
    Disp X
    End

## For

The For (PRGM CTL 4) loops executes a block of commands between the For and End commands n number of times. For is useful when you know the exact number of times you want to repeat a section of code.

### Syntax

* Where variable is a Real (A-Z & θ). This variable represents a counter.
* Where begin is the number to being counting from
* Where end is the number to stop exectution once variable equals end
* Where, optionally, increment is the amount to change variable after each loop. If this argument is not passed, it is assumed to be 1.

### Examples

To print the numbers 1 to 5 using a For loop:
    For(I,1,5)
    Disp I
    End
This code will print:
To traverse a list and print its elements:
    For(I,1,dim(L1))
    Disp L1(I)
    End

## Repeat

The Repeat (PRGM CTL 6) loop executes a block of commands between the Repeat and End commands until specified condition is true. The condition is tested at the beginning of the loop (when the End command is encountered), so if the condition is initially true, the block of commands will never execute.
Repeat is simply While where the condition is inverted.

### Syntax

* Where condition is any statement resulting in a true/false/zero/non-zero result
** If condition returns false or zero, statement continues to execute
** If condition returns true or non-zero, statement will not execute and will skip to after the End

### Examples

The following example demonstrates the use of a Repeat statement. It will continue to ask the user for an X value until X > 5 :
    0→X
    Repeat X>5
    Prompt X
    End

## You try it!

Try these examples to practice using loops.

### Summation from 1 to n

Write a program that asks the user for a number n (must be greater than 1) and prints the sum of the numbers 1 to n. For example, if n = 6, the program would display 21 ($1+2+3+4+5+6=21$).
Solution :
0→N // Clear n
Repeat N>1 // Until n is greater than 1,
Prompt N // Ask for n
End // End repeat loop
0→S // Clear s (sum)
For(X,1,N) // From 1 to n,
S+X→S // Add X to S
End // End for loop
Disp S // Print
Alternate solution using summation
0→N // Clear n
Repeat N>1 // Until n is greater than 1,
Prompt N // Ask for n
End // End repeat loop
Disp Σ(X,X,1,N) // Summation Σ(expression,variable,start,end)
This example uses the following summation expression: $\sum _{i=1}^{N}x_{i}$ :

### Fibonacci Sequence

The Fibonacci Sequence is defined as $F(n)=F(n-1)+F(n-2)$ where $F(1)=0$ and $F(2)=1$. Therefore, the first 10 elements of the sequence are 0, 1, 1, 2, 3, 5, 8, 13, 21, 34. Write a program that stores the first 100 elements of the sequence to L1, then display them. Remember, you will have to instantiate the list first.

### FizzBuzz

FizzBuzz is a children's game often used today as a programming evaluation program. The original game consists of players taking turns to count incrementally, replacing any number divisible by 3 with the word "fizz", and any number divisible by 5 with the word "buzz". For this example, write a program that counts from 1 to 100, replacing numbers divisible by 3 with "Fizz", 5 with "Buzz", and 3 and 5 with "FizzBuzz."
Hint: Take the remainder of the current value and the key numbers and compare it to 0.
You will have to get creative writing this program as there are many ways to approach it. The following solution is just one of many solutions:
Solution :
In this example, we must check multiples of 15 before checking 3 or 5.
:ClrHome
:For(X,1,100)
:If remainder(X,15)=0:Then
:Disp "FIZZBUZZ"
:Else
:If remainder(X,3)=0:Then
:Disp "FIZZ"
:Else
:If remainder(X,5)=0:Then
:Disp "BUZZ"
:Else
:Disp X
:End
:End
:End
:End
Solution without remainder
:ClrHome
:For(X,1,100)
:If fPart(X/15)*15=0:Then
:Disp "FIZZBUZZ"
:Else
:If fPart(X/3)*3=0:Then
:Disp "FIZZ"
:Else
:If fPart(X/5)*5=0:Then
:Disp "BUZZ"
:Else
:Disp X
:End
:End
:End
:End :
Previous: Conditional Statements Next: Advanced Variables Table of Contents: TI-Basic Z80 Programming