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While loop
Control flow statement for repeating execution until a condition is met From Wikipedia, the free encyclopedia
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In computer programming, a while loop is a control flow statement that allows code to be executed repeatedly based on a Boolean condition. The while loop can be thought of as a repeating if statement.
![]() | It has been suggested that Do while loop be merged into this article. (Discuss) Proposed since September 2025. |
This article needs additional citations for verification. (October 2016) |

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Overview
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Perspective
A while consists of a block of code and a conditional expression.[1] The conditional is evaluated, and if true,[1] the block of code is executed. This repeats until the conditional becomes false. Because the while loop checks the conditional before the block is executed, the control structure is also known as a pre-test loop. In contrast, do-while loop tests the conditional after the block.
For example, in the languages C, Java, C#,[2] 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 the loop body is entered, where printf()
is called and x is incremented by 1. After completing the statements in the loop body, the condition, (x < 5), is checked again, and the loop is executed again. This process repeats until x has the value 5.
The condition can always valuate as true to create an infinite loop. In this case, there may be a early-exit 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
}
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Examples
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Perspective
These while loops calculate the factorial of 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 > 1 loop
Factorial := Factorial * Counter;
Counter := Counter - 1;
end loop;
Ada.Integer_Text_IO.Put (Factorial);
end Factorial;
APL
counter ← 5
factorial ← 1
:While counter > 1
factorial ×← counter
counter -← 1
:EndWhile
⎕ ← factorial
or simply
!5
AutoHotkey
counter := 5
factorial := 1
While counter > 1
factorial *= counter--
MsgBox % factorial
Small Basic
counter = 5 ' Counter = 5
factorial = 1 ' initial value of variable "factorial"
While counter > 1
factorial = factorial * counter
counter = counter - 1
EndWhile
TextWindow.WriteLine("Factorial = " + factorial)
Visual Basic
Dim counter As Integer = 5 ' init variable and set value
Dim factorial As Integer = 1 ' initialize factorial variable
Do While counter > 1
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 [ $counter -gt 1 ]; do
factorial=$((factorial * counter))
counter=$((counter - 1))
done
echo $factorial
C, C++
int main() {
int counter = 5;
int factorial = 1;
while (counter > 1) {
factorial *= counter--;
}
printf("%d", factorial);
}
ColdFusion Markup Language (CFML)
Script syntax
counter = 5;
factorial = 1;
while (counter > 1) {
factorial *= counter--;
}
writeOutput(factorial);
Tag syntax
<cfset counter = 5>
<cfset factorial = 1>
<cfloop condition="counter GT 1">
<cfset factorial *= counter-->
</cfloop>
<cfoutput>#factorial#</cfoutput>
Fortran
program FactorialProg
integer :: counter = 5
integer :: factorial = 1
do while (counter > 1)
factorial = factorial * counter
counter = counter - 1
end do
print *, factorial
end program FactorialProg
Go
Go has no while statement, but it has the function of a for statement when omitting some elements of the for statement.
counter, factorial := 5, 1
for counter > 1 {
counter, factorial = counter-1, factorial*counter
}
Java, C#, D
The code for the loop is the same for Java, C# and D:
int counter = 5;
int factorial = 1;
while (counter > 1) {
factorial *= counter--;
}
JavaScript
let counter = 5;
let factorial = 1;
while (counter > 1)
factorial *= counter--;
console.log(factorial);
Lua
counter = 5
factorial = 1
while counter > 1 do
factorial = factorial * counter
counter = counter - 1
end
print(factorial)
MATLAB, Octave
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>1, (*While loop*)
factorial*=counter; (*Multiply*)
counter--; (*Decrement*)
];
factorial
]
Oberon, Oberon-2, Oberon-07, Component Pascal
MODULE Factorial;
IMPORT Out;
VAR
Counter, Factorial: INTEGER;
BEGIN
Counter := 5;
Factorial := 1;
WHILE Counter > 1 DO
Factorial := Factorial * Counter;
DEC(Counter)
END;
Out.Int(Factorial,0)
END Factorial.
Maya Embedded Language
int $counter = 5;
int $factorial = 1;
while ($counter > 1) {
$factorial *= $counter;
$counter -= 1;
}
print("Factorial = " + $factorial + "\n");
Nim
var
counter = 5 # Set counter value to 5
factorial = 1 # Set factorial value to 1
while counter > 1: # While counter is greater than 0
factorial *= counter # Set new value of factorial to counter.
dec counter # Set the counter to counter - 1.
echo factorial
Non-terminating while loop:
while true:
echo "Help! I'm stuck in a loop!"
Pascal
Pascal has two forms of the while loop, while
and repeat-until
. while
repeats one statement (unless enclosed in a begin-end block) as long as the condition is true. repeat-until
repetitively executes a block of one or more statements until the a condition is false. The main difference between the two is that while
executes zero times if the condition is initially false, whereas repeat-until
executes at least once.
program Factorial1;
var
Fv: integer;
procedure fact(counter:integer);
var
Factorial: integer;
begin
Factorial := 1;
while Counter > 1 do
begin
Factorial := Factorial * Counter;
Counter := Counter - 1
end;
WriteLn(Factorial)
end;
begin
Write('Enter a number to return its factorial: ');
readln(fv);
repeat
fact(fv);
Write('Enter another number to return its factorial (or 0 to quit): ');
until fv=0;
end.
Perl
my $counter = 5;
my $factorial = 1;
while ($counter > 1) {
$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 > 1) {
$factorial *= $counter--; // Multiply, then decrement.
}
echo $factorial;
PL/I
The PL/I DO
statement can act as either a for loop, a while loop, or a do until loop.
declare counter fixed initial(5);
declare factorial fixed initial(1);
do while(counter > 1)
factorial = factorial * counter;
counter = counter - 1;
end;
Python
counter = 5 # Set the value to 5
factorial = 1 # Set the value to 1
while counter > 1: # While counter(5) is greater than 0
factorial *= counter # Set new value of factorial to counter.
counter -= 1 # Set the 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 1)
(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 1)
(set! factorial (* factorial counter))
(set! counter (sub1 counter)))
(displayln factorial)
However, an imperative programming style is often discouraged in Scheme and Racket.
Ruby
# Count Down Variant
counter = 5
factorial = 1
while counter > 1
factorial *= counter
counter -= 1
end
puts factorial
# Count Up Variant
counter = 2
factorial = 1
while counter <= 5
factorial *= counter
counter += 1
end
puts factorial
Rust
fn main() {
let mut counter = 5;
let mut factorial = 1;
while counter > 1 {
factorial *= counter;
counter -= 1;
}
println!("{}", 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 initial counter value to 5
var factorial = 1 // Set the initial factorial value to 1
while counter > 1 { // 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 > 1} {
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);
PowerShell
$counter = 5
$factorial = 1
while ($counter) {
$factorial *= $counter--
}
$factorial
While (language)
While[3] is a simple programming language constructed from assignments, sequential composition, conditionals, and while statements, used in the theoretical analysis of imperative programming language semantics.[4][5]
C := 5;
F := 1;
while (C > 1) do
F := F * C;
C := C - 1;
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See also
- Do while loop
- For loop
- Foreach
- Primitive recursive function
- General recursive function
- LOOP (programming language) – a programming language with the property that the functions it can compute are exactly the primitive recursive functions
References
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