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While Loop

Explore how to use while loops in Perl to repeat code blocks based on conditions. Understand the syntax and execution flow, and learn to prevent infinite loops by managing loop variables effectively.

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What is a while loop?

The while loop consists of a condition. If the condition is true, then the body of the loop is executed and the condition is checked again. This process is repeated until the condition becomes false. The syntax is as follows:

The curly braces surrounding the body of the while loop indicate that multiple statements can be executed as part of this loop.

Example

Here’s a look at the while loop code:

Perl
$x=4;
$y=0;
while ( $y <= 10 ) {   # the while loop will run till y<=10 condition is being met               
$y += $x;
$x += 1;
} #the loop will iterate 3 times
print "the value of x is: $x\n";
print "the value of y is: $y\n";

Explanation

Below is an illustration of the code above to help us better understand this logic.

If the variable(s) involved in the while loop condition do not change while it executes, then the loop condition would either always be true, or always be false. If the loop condition is always true, this creates an infinite loop. This is demonstrated in the following example:

Perl
$y = 0;
$x = 4;
while ( $y <= 10 ) { #since y is not being changed inside the while loop you will get stuck 
  $x += 1;           # in an infinite loop as the condition will always be met 
}
$y += $x;

According to what is written, even though the second line after the while was incremented, only the first line corresponds to the while loop. This is a huge problem, because the variable involved in the condition (＄y <= 10), i.e. ＄y, does not change, so it will always evaluate to “true”, making this an​ infinite loop. We can follow the above example and its advice to always make sure that we don’t have an infinite loop.