Loops & Iteration — PHP Course

What you'll learn

Loops apply an operation repeatedly. You'll learn each PHP loop, iterate real nested data, implement common algorithms, and avoid a reference bug that catches experienced developers.

Choose between while, do-while, for, and foreach
Iterate array keys and values
Skip or stop work deliberately
Accumulate totals and counts
Recognize when an array function is clearer

while and do-while

A while loop checks before each iteration. A do...while checks after, so its body always runs at least once.

countdown.php

<?php

$seconds = 3;

while ($seconds > 0) {
    echo $seconds . PHP_EOL;
    $seconds--;
}

echo 'Launch!';

Every while loop needs progress

If the condition can stay true forever, the loop never ends. Identify which statement moves the state toward termination before you run it.

for loops

A for loop keeps initialization, condition, and update together. It is useful when the iteration count or index is central to the task.

multiples.php

<?php

for ($i = 1; $i <= 5; $i++) {
    echo ($i * 3) . PHP_EOL;
}

foreach is the default for arrays

foreach communicates that you care about each element rather than index arithmetic. Ask for the key only when it adds value.

course-list.php

<?php

$courses = [
    ['title' => 'PHP Foundations', 'minutes' => 40],
    ['title' => 'Web Fundamentals', 'minutes' => 46],
    ['title' => 'Modern PHP', 'minutes' => 50],
];

foreach ($courses as $index => $course) {
    $number = $index + 1;
    echo "{$number}. {$course['title']} ({$course['minutes']} min)" . PHP_EOL;
}

Need	Best starting point
Repeat until a condition changes	`while`
Run at least once, then check	`do...while`
Use an explicit numeric counter	`for`
Visit every item in an array	`foreach`

break and continue

search.php

<?php

$ids = [0, 18, 27, 42, 55];

foreach ($ids as $id) {
    if ($id <= 0) {
        continue; // skip invalid values
    }

    if ($id === 42) {
        echo 'Found record 42';
        break; // stop searching
    }
}

continue skips to the next iteration. break exits the loop. Both are useful when they make a rule explicit; too many exit points can make flow harder to trace.

Accumulate useful results

Many loop algorithms maintain one or more accumulators: a running total, count, minimum, maximum, or grouped result.

orders.php

<?php

$orders = [42.50, 18.00, 120.75, 9.99];
$total = 0.0;
$largeOrders = 0;

foreach ($orders as $amount) {
    $total += $amount;

    if ($amount >= 100) {
        $largeOrders++;
    }
}

echo 'Total: $' . number_format($total, 2) . PHP_EOL;
echo "Large orders: {$largeOrders}";

Tip

After a loop works, ask whether array_sum(), array_filter(), or another focused function expresses the intent more directly. Keep the loop when multiple related results are calculated in one pass.

The foreach reference trap

references.php

<?php

$scores = [10, 20, 30];

foreach ($scores as &$score) {
    $score += 5;
}
unset($score); // break the lingering reference

print_r($scores);

Watch out

A referenced foreach variable stays bound to the last element after the loop. Always unset() it immediately—or prefer building a transformed array without references.

Recap & quick check

Key takeaways

while checks before; do-while runs at least once; for highlights counters; foreach visits array items.
Use key => value only when the key matters.
continue skips an iteration and break ends the loop.
Accumulators calculate totals, counts, minima, maxima, and grouped results.
Unset a foreach reference immediately after the loop.

Quick check

1. Which loop is usually clearest for visiting every array item?

2. What does continue do?

3. Why unset a referenced foreach variable?