PHP While Loops

Loops let you repeat code multiple times. The while loop is PHP's simplest loop - it keeps executing as long as a condition remains true. Perfect when you don't know in advance how many iterations you'll need.

While Loop Syntax

The while loop checks the condition before each iteration:

<?php
while (condition) {
    // Code to repeat
    // Make sure condition eventually becomes false!
}
?>

Click Run to execute your code

Basic While Loop Examples

<?php
// Counting up
$i = 1;
while ($i <= 5) {
    echo "Number: $i\n";
    $i++;  // Don't forget this!
}

// Counting down
$countdown = 5;
while ($countdown > 0) {
    echo "$countdown... ";
    $countdown--;
}
echo "Liftoff!\n";

// Processing until empty
$queue = ["Task 1", "Task 2", "Task 3"];
while (count($queue) > 0) {
    $task = array_shift($queue);  // Remove first element
    echo "Processing: $task\n";
}
?>

Do-While Loop

The do-while loop checks the condition after each iteration, guaranteeing at least one execution:

<?php
do {
    // Code to repeat (runs at least once)
} while (condition);  // Note the semicolon!
?>

Click Run to execute your code

While vs Do-While

<?php
$value = 100;

// While: Won't execute (condition false initially)
while ($value < 10) {
    echo "While: $value\n";
    $value++;
}

// Do-while: Executes once despite false condition
do {
    echo "Do-while: $value\n";
    $value++;
} while ($value < 10);
?>

Practical Use Cases

Reading File Lines

<?php
$file = fopen("data.txt", "r");
while (($line = fgets($file)) !== false) {
    echo $line;
}
fclose($file);
?>

Database Result Processing

<?php
$result = $mysqli->query("SELECT name FROM users");
while ($row = $result->fetch_assoc()) {
    echo "User: " . $row['name'] . "\n";
}
?>

Retry Logic with Backoff

<?php
$maxRetries = 3;
$attempt = 0;
$success = false;

while ($attempt < $maxRetries && !$success) {
    $attempt++;
    echo "Attempt $attempt... ";

    // Simulate operation that might fail
    $success = (rand(1, 3) === 1);

    if ($success) {
        echo "Success!\n";
    } else {
        echo "Failed. Retrying...\n";
        sleep(1);  // Wait before retry
    }
}

if (!$success) {
    echo "All $maxRetries attempts failed.\n";
}
?>

Infinite Loops

Sometimes you intentionally want an infinite loop, exiting with break:

<?php
// Infinite loop pattern
while (true) {
    $input = readline("Enter command (quit to exit): ");

    if ($input === "quit") {
        break;  // Exit the loop
    }

    echo "You entered: $input\n";
}

echo "Goodbye!\n";
?>

Alternative Syntax

While loops have an alternative syntax for templates:

<?php $items = ["Apple", "Banana", "Cherry"]; $i = 0; ?>

<ul>
<?php while ($i < count($items)): ?>
    <li><?= $items[$i] ?></li>
    <?php $i++; ?>
<?php endwhile; ?>
</ul>

Common Mistakes

<?php
$i = 1;

// ❌ WRONG: Infinite loop! $i never changes
while ($i <= 5) {
    echo $i;
    // Missing: $i++
}

// ✅ CORRECT: Increment the counter
while ($i <= 5) {
    echo $i;
    $i++;
}
?>

<?php
$items = [1, 2, 3, 4, 5];
$i = 0;

// ❌ WRONG: <= causes index out of bounds
while ($i <= count($items)) {  // 0,1,2,3,4,5 (6 iterations!)
    echo $items[$i];  // Error on last iteration
    $i++;
}

// ✅ CORRECT: Use < for zero-indexed arrays
while ($i < count($items)) {  // 0,1,2,3,4 (5 iterations)
    echo $items[$i];
    $i++;
}
?>

<?php
// ❌ WRONG: Missing semicolon causes syntax error
do {
    echo "Hello";
} while (false)  // Missing semicolon!

// ✅ CORRECT: Always end with semicolon
do {
    echo "Hello";
} while (false);
?>

Exercise: Number Guessing Game

<?php
$target = rand(1, 10);
$maxAttempts = 5;
$attempts = 0;
$won = false;

// Simulated guesses
$guesses = [5, 3, 7, 8, 6, 4, 9, 2, 10, 1];

echo "Guess a number between 1 and 10!\n";
echo "(Secret number: $target)\n\n";

while ($attempts < $maxAttempts && !$won) {
    $guess = $guesses[$attempts];
    $attempts++;

    echo "Attempt $attempts: Guessing $guess... ";

    if ($guess === $target) {
        $won = true;
        echo "Correct!\n";
    } elseif ($guess < $target) {
        echo "Too low!\n";
    } else {
        echo "Too high!\n";
    }
}

echo "\n";
if ($won) {
    echo "You won in $attempts attempt(s)!\n";
} else {
    echo "Game over! The number was $target.\n";
}
?>

Summary

What's Next?

While loops are great for unknown iteration counts. Next, let's explore For Loops - the go-to choice when you know exactly how many times to repeat!