PHP for Loop: Syntax, Arrays, break and continue

for ($i = 0; $i < 5; $i++) { ... } runs the block a fixed number of times. The three parts are the start ($i = 0, runs once), the condition ($i < 5, checked before every pass) and the step ($i++, runs after every pass). The loop ends as soon as the condition is false.

<?php
for ($i = 1; $i <= 5; $i++) {
    echo "Pass $i\n";
}

echo "After the loop, \$i is $i\n";

$i still exists after the loop and holds the value that made the condition false (6). PHP has no block scope for loop variables.

Loop through an array with an index

For a list with keys 0, 1, 2 ..., the counter doubles as the index. Store count() in a variable first so it is not called again on every pass.

<?php
$fruits = ['apple', 'banana', 'cherry', 'date'];

for ($i = 0, $n = count($fruits); $i < $n; $i++) {
    echo $i + 1, ". ", $fruits[$i], "\n";
}

// The index makes neighbours easy to reach
for ($i = 1, $n = count($fruits); $i < $n; $i++) {
    echo $fruits[$i - 1], " comes before ", $fruits[$i], "\n";
}

The first part can hold several expressions separated by commas, which is how $n = count($fruits) gets set once. When you only need each value (and not its neighbours), foreach is shorter and also works on arrays whose keys are not 0 to n - 1.

Count down and step by more than 1

The step can be any expression: $i-- to count down, $i += 2 for every second number, $i *= 2 for powers of two.

<?php
for ($i = 5; $i >= 1; $i--) {
    echo $i, " ";
}
echo "liftoff\n";

for ($i = 0; $i <= 20; $i += 5) {
    echo $i, " ";
}
echo "\n";

for ($i = 1; $i <= 1000; $i *= 2) {
    echo $i, " ";
}
echo "\n";

// Every second element of an array
$letters = range('a', 'h');
for ($i = 0; $i < count($letters); $i += 2) {
    echo $letters[$i];
}
echo "\n";

range('a', 'h') builds the array ['a', 'b', ... 'h']. With range(1, 10) and foreach you get the same counting as a for loop, at the cost of building the whole array first.

break and continue

break ends the loop right away. continue skips the rest of the current pass and jumps to the step and the next condition check.

<?php
// Print odd numbers, stop at the first one above 12
for ($i = 1; $i <= 100; $i++) {
    if ($i % 2 === 0) {
        continue;       // skip even numbers
    }
    if ($i > 12) {
        break;          // leave the loop
    }
    echo $i, " ";
}
echo "\n";

// Find the first multiple of 7 above 50
for ($n = 51; ; $n++) {
    if ($n % 7 === 0) {
        echo "Found $n\n";
        break;
    }
}

The second loop has an empty condition, which means "always true", so it runs until break. In nested loops, break 2 and continue 2 act on the outer loop, as the next example shows.

Nested for loops: a multiplication table

A loop inside a loop runs the inner loop completely for every pass of the outer one. Here the output is HTML, so the Page tab shows a real table.

<?php
$size = 9;
?>
<style>
    table { border-collapse: collapse; font-family: sans-serif; }
    td, th { border: 1px solid #ccc; padding: 4px 8px; text-align: right; }
    th { background: #f0f0f0; }
</style>
<table>
    <tr>
        <th>×</th>
        <?php for ($col = 1; $col <= $size; $col++): ?>
            <th><?= $col ?></th>
        <?php endfor; ?>
    </tr>
    <?php for ($row = 1; $row <= $size; $row++): ?>
        <tr>
            <th><?= $row ?></th>
            <?php for ($col = 1; $col <= $size; $col++): ?>
                <td><?= $row * $col ?></td>
            <?php endfor; ?>
        </tr>
    <?php endfor; ?>
</table>

Change $size to 12 and run it again. The for (...): and endfor; form is the alternative syntax that keeps loops readable between HTML tags. The same table built as plain text, and with break 2 to stop both loops:

<?php
for ($row = 1; $row <= 5; $row++) {
    for ($col = 1; $col <= 5; $col++) {
        if ($row * $col > 12) {
            echo "\nStopped at $row × $col\n";
            break 2;    // leave both loops
        }
        echo str_pad($row * $col, 4, ' ', STR_PAD_LEFT);
    }
    echo "\n";
}

Common mistakes: off by one and the endless loop

The two classic for bugs: using <= with count() reads one element past the end, which PHP reports as Warning: Undefined array key 3 and treats as null; and a step that never moves the counter toward the end ($i-- where you meant $i++) keeps the condition true forever.

<?php
$items = ['pen', 'ink', 'paper'];

// Wrong: $i <= count($items) also tries index 3
// for ($i = 0; $i <= count($items); $i++) { ... }

// Right: < count for indexes 0 to count - 1
for ($i = 0; $i < count($items); $i++) {
    echo "[$i] {$items[$i]}\n";
}

// Last element without a loop
echo "Last: ", $items[count($items) - 1], "\n";

For loops whose length you cannot know in advance, such as reading until a file ends, a while loop fits better.