PHP Foreach Loops

The foreach loop is PHP's most elegant way to iterate arrays. It automatically handles array traversal without needing counters or indices - just loop through each element directly!

Foreach Syntax

There are two forms of foreach - with values only, or with keys and values:

<?php
// Values only
foreach ($array as $value) {
    // Use $value
}

// Keys and values
foreach ($array as $key => $value) {
    // Use $key and $value
}
?>

Click Run to execute your code

Indexed Arrays

For simple indexed arrays, you usually just need the values:

<?php
$fruits = ["Apple", "Banana", "Cherry"];

// Simple iteration
foreach ($fruits as $fruit) {
    echo "I like $fruit\n";
}

// With index (key)
foreach ($fruits as $index => $fruit) {
    $position = $index + 1;
    echo "$position. $fruit\n";
}
// Output:
// 1. Apple
// 2. Banana
// 3. Cherry
?>

Associative Arrays

For associative arrays, the key-value syntax is essential:

<?php
$user = [
    "name" => "John",
    "email" => "[email protected]",
    "role" => "admin"
];

foreach ($user as $field => $value) {
    echo ucfirst($field) . ": $value\n";
}
// Output:
// Name: John
// Email: [email protected]
// Role: admin
?>

Nested Arrays

Foreach handles nested arrays elegantly:

<?php
$products = [
    ["name" => "Laptop", "price" => 999.99],
    ["name" => "Mouse", "price" => 29.99],
    ["name" => "Keyboard", "price" => 79.99]
];

foreach ($products as $product) {
    echo "{$product['name']}: ${$product['price']}\n";
}

// With nested foreach
$categories = [
    "Electronics" => ["TV", "Radio", "Phone"],
    "Clothing" => ["Shirt", "Pants", "Hat"]
];

foreach ($categories as $category => $items) {
    echo "\n$category:\n";
    foreach ($items as $item) {
        echo "  - $item\n";
    }
}
?>

Modifying Values by Reference

Use & to modify array elements in place:

Click Run to execute your code

Reference Syntax

<?php
$numbers = [1, 2, 3, 4, 5];

// Without reference - original unchanged
foreach ($numbers as $num) {
    $num *= 2;  // Modifies copy only
}
// $numbers is still [1, 2, 3, 4, 5]

// With reference - modifies original
foreach ($numbers as &$num) {
    $num *= 2;  // Modifies actual array element
}
unset($num);  // CRITICAL: Remove reference!
// $numbers is now [2, 4, 6, 8, 10]
?>

Foreach vs For Loop

<?php
$colors = ["red", "green", "blue"];

// Foreach (recommended for arrays)
foreach ($colors as $color) {
    echo "$color ";
}

// For loop equivalent (verbose)
for ($i = 0; $i < count($colors); $i++) {
    echo $colors[$i] . " ";
}
?>

Alternative Syntax

For templates mixing PHP and HTML:

<?php $users = [
    ["name" => "Alice", "active" => true],
    ["name" => "Bob", "active" => false]
]; ?>

<ul>
<?php foreach ($users as $user): ?>
    <li class="<?= $user['active'] ? 'active' : 'inactive' ?>">
        <?= htmlspecialchars($user['name']) ?>
    </li>
<?php endforeach; ?>
</ul>

Common Mistakes

<?php
$arr = [1, 2, 3];

// ❌ WRONG: Missing unset()
foreach ($arr as &$val) {
    $val *= 2;
}
// $val still references $arr[2]!

$val = 100;  // Oops! Changes $arr[2] to 100!
print_r($arr);  // [2, 4, 100] - unexpected!

// ✅ CORRECT: Always unset
foreach ($arr as &$val) {
    $val *= 2;
}
unset($val);  // Break the reference
?>

<?php
$items = ["a", "b", "c", "d"];

// ❌ DANGEROUS: Adding elements while iterating
foreach ($items as $item) {
    if ($item === "b") {
        $items[] = "e";  // Don't do this!
    }
}

// ✅ SAFE: Build a new array instead
$newItems = [];
foreach ($items as $item) {
    $newItems[] = $item;
    if ($item === "b") {
        $newItems[] = "e";
    }
}
?>

<?php
$data = ["name" => "John", "age" => 30];

// ❌ WRONG: Only gets values
foreach ($data as $value) {
    // Can't access the key here!
}

// ✅ CORRECT: Get both key and value
foreach ($data as $key => $value) {
    echo "$key: $value\n";
}
?>

Exercise: Data Processor

<?php
$products = [
    ["name" => "Laptop", "price" => 999.99, "qty" => 2],
    ["name" => "Mouse", "price" => 29.99, "qty" => 10],
    ["name" => "Keyboard", "price" => 79.99, "qty" => 5],
    ["name" => "Monitor", "price" => 299.99, "qty" => 3]
];

$totalValue = 0;
$mostExpensive = null;
$highestPrice = 0;

// Process products
foreach ($products as &$product) {
    // Calculate line total
    $lineTotal = $product['price'] * $product['qty'];
    $totalValue += $lineTotal;

    // Track most expensive
    if ($product['price'] > $highestPrice) {
        $highestPrice = $product['price'];
        $mostExpensive = $product['name'];
    }

    // Apply discount to items over $50
    if ($product['price'] > 50) {
        $product['price'] *= 0.85;  // 15% off
        $product['discounted'] = true;
    }
}
unset($product);

echo "=== Product Report ===\n\n";
foreach ($products as $product) {
    $status = isset($product['discounted']) ? " (15% OFF!)" : "";
    printf("%-10s: $%7.2f x %d%s\n",
        $product['name'],
        $product['price'],
        $product['qty'],
        $status
    );
}

echo "\nTotal Inventory Value: $" . number_format($totalValue, 2) . "\n";
echo "Most Expensive Item: $mostExpensive\n";
?>

Summary

What's Next?

You've learned all PHP loop types! Now let's master Loop Control with break and continue to precisely control loop execution!