Loops

A loop allows a block of code to repeat some number of times. Depending on the type of loop, it can repeat a set number of times, until a particular condition is no longer met, or once for each member of an array. The process of repeating the code block is called iteration.

for Loop

A for loop is used in PHP when it is known how many times its bock of code should execute. The syntax looks like this:

for (init; test; increment) {
  code to execute;
}

• init: Initialize a counter variable.
• test: Tests the counter variable. The loop continues to iterate as long as this test evaluates to true.
• increment: Increment/decrements the counter variable. Executed on each loop iteration.
• code to execute: Block of code to execute on each iteration. The counter variable is available inside this block.

The order these pieces are executed are: init, test, execute, increment, then back to test.

Note that it’s possible to write a for loop that never executes if the initial test fails.

Example

<?php
for ($i = 1;$i <= 10; $i++) {
    echo 'iteration #' . $i . '<br/>';
    }
?>

Output:

iteration #1
iteration #2
iteration #3
iteration #4
iteration #5
iteration #6
iteration #7
iteration #8
iteration #9
iteration #10

foreach Loop

A foreach loop iterates through a block of code once for each element of an array. The syntax is as follows:

Iterate through array values:

foreach ($array as $value) {
  code to execute;
}

• $array: An array variable.
• $value: Variable to receive each value of array in turn.
• execute: Block of code to execute on each iteration. The $value variable is available inside this block.

Iterate through array keys and values:

foreach ($array as $key => $value) {
  code to execute;
}

• $array: An array variable.
• $key: Variable to receive each key of array in turn.
• $value: Variable to receive each value of array in turn.
• code to execute: Block of code to execute on each iteration. The $key and $value variables are available inside this block.

Examples

Values only:

<?php
$a = ['one','two','three','four'];

foreach ($a as $x) {
  echo 'The value is ' . $x . '<br />';
  }
?>

Output:

The value is one
The value is two
The value is three
The value is four

Values and keys:

<?php
$a = ['one' => 'green','two' => 'blue','three' => 'red','four' => 'yellow'];

foreach ($a as $k => $x) {
  echo 'The value for ' . $k . ' is ' . $x . '<br />';
  }
?>

Output:

The value for one is green
The value for two is blue
The value for three is red
The value for four is yellow

while Loop

The while loop iterates through a block of code as long as a condition evaluates to true. The syntax looks like this:

while (test) {
  code to execute;
}

• test: The expression to evaluate on each iteration of loop. Iterations continue until this evaluates to false.
• code to execute: Block of code to execute on each iteration.

Example

<?php
$x = 0;
$i = 2;

while ($x <= 100) {
    echo 'the number is ' . $x . '<br/>';
    $x += $i;
    $i *= 2;
    }
?>

Output:

the number is 0
the number is 2
the number is 6
the number is 14
the number is 30
the number is 62

do...while Loop

The do...while loop, like a while loop, iterates as long as a condition is true. But the do...while loop tests the condition after the iteration, not before, so the loop always executes at least once.

The syntax looks like this:

do {
  execute;
  } while (test);

• test: The expression to evaluate on each iteration of loop. Iterations continue until this evaluates to false.
• execute: Block of code to execute on each iteration.

Example

<?php
$x = 125;

do {
    echo 'the number is ' . $x . '<br/>';
    $x++;
    } while ($x <= 100);
?>

Output:

the number is 125

break Statement

The break statement can be used to prematurely jump out of a loop during execution.

Example

<?php
$x = 0;
$i = 2;

while ($x <= 100) {
    echo 'the number is ' . $x . '<br/>';
    if ($x == 14) { break; }
    $x += $i;
    $i *= 2;
    }
?>

Output:

the number is 0
the number is 2
the number is 6
the number is 14

continue Statement

The continue statement breaks out of the current loop and immediately starts the next iteration.

Example

<?php
for ($i = 1;$i <= 10; $i++) {
    if ($i % 2 == 1) {continue; }
    echo 'iteration #' . $i . '<br/>';
    }
?>

Output:

iteration #2
iteration #4
iteration #6
iteration #8
iteration #10