Loops: while, for and foreach

Loops run the same block of code several times. Listing products, sending a batch of emails, reading lines from a file: all loops.

while

A while loop repeats as long as its condition is true:

<?php

$countdown = 3;

while ($countdown > 0) {
    echo $countdown, PHP_EOL;
    $countdown--;
}

echo 'Lift off!';

3
2
1
Lift off!

The condition is checked before each pass. If it is false from the start, the body never runs.

do-while

do-while checks the condition after the body, so the body always runs at least once:

<?php

do {
    $roll = random_int(1, 6);
    echo "Rolled {$roll}", PHP_EOL;
} while ($roll !== 6);

for

for is ideal when you know how many times to repeat. It packs the setup, condition and update into one line:

<?php

for ($i = 1; $i <= 5; $i++) {
    echo "Line {$i}", PHP_EOL;
}

The three parts are:

1. $i = 1 runs once, before the loop starts.
2. $i <= 5 is checked before each pass.
3. $i++ runs after each pass.

You can count in other steps too: for ($i = 10; $i >= 0; $i -= 2) counts down in twos.

foreach: the loop you will use most

foreach walks through every element of an array without managing an index:

<?php

$languages = ['PHP', 'JavaScript', 'Python'];

foreach ($languages as $language) {
    echo $language, PHP_EOL;
}

To get keys as well as values, use key => value:

<?php

$prices = [
    'coffee' => 2.80,
    'tea' => 2.20,
    'cake' => 3.50,
];

foreach ($prices as $item => $price) {
    printf("%-8s £%.2f\n", $item, $price);
}

coffee   £2.80
tea      £2.20
cake     £3.50

For indexed arrays, the key is the position, which is handy for numbering:

<?php

$steps = ['Install PHP', 'Write a script', 'Run it'];

foreach ($steps as $index => $step) {
    echo ($index + 1) . ". {$step}", PHP_EOL;
}

break and continue

continue skips the rest of the current pass. break leaves the loop entirely:

<?php

$numbers = [4, 7, -1, 12, 0, 9];

foreach ($numbers as $n) {
    if ($n < 0) {
        continue; // Ignore negative numbers.
    }

    if ($n === 0) {
        break; // Zero marks the end of the data.
    }

    echo $n, PHP_EOL;
}

4
7
12

Loops in HTML templates

In templates, PHP has an alternative syntax that reads better between HTML tags:

<?php $todos = ['Buy milk', 'Learn loops', 'Walk the dog']; ?>

<ul>
    <?php foreach ($todos as $todo): ?>
        <li><?= htmlspecialchars($todo) ?></li>
    <?php endforeach; ?>
</ul>

htmlspecialchars() escapes the text so it cannot break your HTML. You will see why that matters in the forms lesson.

Which loop should I use?

Summary

• while repeats while a condition is true; make sure something changes it.
• do-while always runs at least once.
• for suits counting; foreach suits arrays and is the most common.
• continue skips a pass, break exits the loop.
• Use foreach (...): and endforeach; inside HTML templates.