PHP Loops

for ($i = 1; $i <= 5; $i++) {
    echo "Row $i<br>";
}

The three parts are the start ($i = 1), the condition checked before each pass ($i <= 5) and the update after each pass ($i++). Use a for loop when you know how many times to repeat.

$tickets = 3;
while ($tickets > 0) {
    echo "Selling ticket $tickets\n";
    $tickets--;
}

while checks its condition before each pass. do { ... } while (condition); checks after, so it always runs at least once. As with any while loop, make sure something inside it eventually makes the condition false.

foreach visits every item of an array, one at a time:

$colours = ["red", "green", "blue"];
foreach ($colours as $colour) {
    echo "<li>$colour</li>";
}

To get the key (position or name) as well as the value, use as $key => $value:

foreach ($colours as $i => $colour) {
    echo "$i: $colour\n";
}

You'll learn much more about arrays and their keys in the next lesson.

A common pattern is to open an HTML element, loop to create its children, then close it:

<ul>
<?php foreach ($menu as $item): ?>
  <li><?= $item ?></li>
<?php endforeach; ?>
</ul>

This alternative syntax, with a colon and endforeach, is popular in templates because it keeps HTML readable. There are matching endfor, endwhile and endif keywords.

You can put one loop inside another. The inner loop runs all the way through for every single pass of the outer loop, which is how you build anything with rows and columns, such as a seating plan or a table:

$rows = ["A", "B"];
for ($r = 0; $r < count($rows); $r++) {
    for ($seat = 1; $seat <= 3; $seat++) {
        echo $rows[$r] . $seat . " ";
    }
    echo "\n";
}

This prints A1 A2 A3 on the first line and B1 B2 B3 on the second. Give each loop its own variable name ($r and $seat here). Reusing $i in both loops is a classic bug, because the inner loop changes the counter the outer loop depends on.

By default, foreach hands you a copy of each value, so changing it inside the loop doesn't touch the array. Put & in front of the variable to work on the real item instead:

$prices = [10, 20, 30];
foreach ($prices as &$price) {
    $price = $price * 1.2;
}
unset($price); // break the reference when you're done

The unset() line matters. After the loop, $price still points at the last item, and a later loop that reuses the name would overwrite it by accident.

• Use foreach whenever you're walking through an array. It's the shortest and hardest to get wrong, since there's no counter to manage.
• Use for when you need a counter, such as printing numbers 1 to 10 or stepping through every second item.
• Use while when you don't know in advance how many passes you need, for example reading lines from a file until there are none left.
• Use do-while for the rare case where the body must run once before the check, such as showing a menu before asking whether to show it again.