PHP do…while Loop

A do...while loop is like while, but it checks the condition after the block. So the block always runs at least once.

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<?php
$number = 10;

do {
    echo "Number is $number\n";
    $number++;
} while ($number <= 3);

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Number is 10

The condition 10 <= 3 is false, but the block already ran once.

Compare it with while, which would print nothing here.

Notice the semicolon

A do...while ends with a semicolon after the condition. Forgetting it is a syntax error.

When to use it

Use do...while when the work must happen once before you can decide whether to repeat. Typical examples are “ask, then check the answer”, “try, then check if it worked” and menus.

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<?php
$attempts = 0;

do {
    $attempts++;
    $success = $attempts >= 3; // pretend the third try works
    echo "Attempt $attempts: " . ($success ? "ok" : "failed") . "\n";
} while (!$success && $attempts < 5);

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3

Attempt 1: failed
Attempt 2: failed
Attempt 3: ok

Generate a unique code

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<?php
$taken = ["A1", "A2"];
$candidates = ["A1", "A2", "A3"];
$i = 0;

do {
    $code = $candidates[$i++];
} while (in_array($code, $taken, true));

echo "Free code: $code";

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Free code: A3