While Loop

Loops are used to execute a code block many times.

Syntax

while(condition) { // Code fragment to execute. }

Example

A loop can be used to print all numbers in certain range. Like from 1 to 10

<?php $num = 1; while ($num <= 10) { echo $num . " "; $num++; }

Output:

1 2 3 4 5 6 7 8 9 10

At line 4 the condition of the loop is set. Since num is less than 10 the loop executes.

In order to print the numbers to 10, num increases by 1 at line 6.

The loop ends when num reaches value of 11.

Infinite Loop

Infinite Loop has a condition that's always true.

It can be created due to development mistake or used in advanced algorithm.

Here are examples:

<?php $num = 1; while ($num < 5) { echo $num . " "; }

Output:

1 1 1 1 1 1 1 1 1 ...

Since num is never changed, the condition $num < 5 is always true and the loop executes infinitely (or until the program takes more ram than it is allowed).

In order to end the loop num needs to be incremented (like $num++) inside the loop's body.

<?php $num = 1; while (true) { echo "infinite "; }

Output:

infinite infinite infinite infinite infinite ...

Since the condition at line 4 is always true, the loop keeps on repeating.