PHP 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/>';
    }
?>

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Output:

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

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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 />';
  }
?>

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Output:

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

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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 />';
  }
?>

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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

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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;
    }
?>

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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

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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);
?>

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Output:

the number is 125

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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;
    }
?>

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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/>';
    }
?>

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Output:

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