PHP while Loops

Table of Contents

• Introduction
• Syntax of the while Loop
• Using the while Loop

Introduction

Often, you want the same block of code to run over and over again a certain number of times. Instead of adding the same chunk of code into your script, we can use loops. Loops are used to execute the same block of code again and again, as long as a certain condition is true.

PHP loops come in the following flavors:

We discuss the while loop in this article and consider the rest in subsequent sections.

Syntax of the while Loop

The while loop executes a block of code as long as a certain specified condition is true. The syntax of the while loop is given as:

Syntax

1while (expression) {
2    statement(s);
3}

• The while loop tells PHP to execute the nested statement(s) repeatedly, as long as the expression evaluates to true.
• The value of the expression is checked each time at the beginning of the loop, so even if this value changes during the execution of the nested statement(s), execution will not stop until the end of the iteration.
• If the while expression evaluates to false from the very beginning, the nested statement(s) won’t even be run once.

There is also an alternative syntax.

Syntax

1while (expression):
2    statement(s);
3endwhile;

where the colon : and endwhile; replace the braces.

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Using the while Loop

Example

1<?php
2    $i = 1;
3    while ($i <= 10) {
4        echo $i++;  // post-increment
5    }
6?>

12345678910

In the above example, the line echo $i++ prints out the value of $i before incrementing (see post-increment). In the beginning, it prints out 1, then $i increases to 2 and the loop repeats until $i becomes 10. The statement echo $i++ then prints out 10 and $i increases to 11 afterwhich the expression evaluates to false and the loop stops.

Example

1<?php
2    $count = 1;
3    while ($count <= 10){
4        echo "$count times 3 is " . $count * 3 . "<br>";
5        ++$count;
6    }
7?>

1 times 3 is 3
2 times 3 is 6
3 times 3 is 9
4 times 3 is 12
5 times 3 is 15
6 times 3 is 18
7 times 3 is 21
8 times 3 is 24
9 times 3 is 27
10 times 3 is 30

Note that it is immaterial whether we had used ++$count or $count++ in the last statement within the loop.

The next example illustrates a shortened version where the use of ++$count or $count++ will have a bearing on the results.

Example

1<?php
2    $count = 0;
3    while (++$count <= 10)
4        echo "$count times 3 is " . $count * 3 . "<br>";
5?>

1 times 3 is 3
2 times 3 is 6
3 times 3 is 9
4 times 3 is 12
5 times 3 is 15
6 times 3 is 18
7 times 3 is 21
8 times 3 is 24
9 times 3 is 27
10 times 3 is 30

In the above example, $count starts with the value of 0. The expression ++$count <= 10 means that PHP first increases the value of $count by 1 before evaluating the boolean expression.

On the other hand, had we used $count++, we will need to modify the boolean expression as $count++ <= 9. This means that PHP first evaluates the boolean expression before increasing the value of $count by 1.

Example

1<?php
2    $count = 0;
3    while ($count++ <= 9)
4        echo "$count times 3 is " . $count * 3 . "<br>";
5?>

1 times 3 is 3
2 times 3 is 6
3 times 3 is 9
4 times 3 is 12
5 times 3 is 15
6 times 3 is 18
7 times 3 is 21
8 times 3 is 24
9 times 3 is 27
10 times 3 is 30