Working with Loops in PHP

Loops allow you to iterate over arrays and perform repetitive operations efficiently. Instead of writing 100 lines of code to process 100 items, you write one loop that repeats 100 times.

Types of Loops in PHP

1. The `foreach` Loop

The foreach loop is ideal for arrays, automatically iterating through each element without manual index management.

Indexed Arrays

$fruits = ['Apple', 'Banana', 'Orange', 'Mango'];

foreach ($fruits as $fruit) {
    echo $fruit . "\n";
}

// Output:
// Apple
// Banana
// Orange
// Mango

Associative Arrays

Access both keys and values using $key => $value syntax:

$student = [
    'name' => 'John Doe',
    'age' => 20,
    'major' => 'Computer Science',
    'gpa' => 3.8
];

foreach ($student as $key => $value) {
    echo "$key: $value\n";
}

// Output:
// name: John Doe
// age: 20
// major: Computer Science
// gpa: 3.8

Practical Example: Shopping Cart

$cart = [
    'laptop' => 999.99,
    'mouse' => 25.50,
    'keyboard' => 75.00,
    'monitor' => 299.99
];

$total = 0;

foreach ($cart as $item => $price) {
    echo "$item: $" . number_format($price, 2) . "\n";
    $total += $price;
}

echo "Total: $" . number_format($total, 2);

// Output:
// laptop: $999.99
// mouse: $25.50
// keyboard: $75.00
// monitor: $299.99
// Total: $1400.48

2. The `for` Loop

Use when you need index positions or precise iteration control.

$colors = ['Red', 'Green', 'Blue', 'Yellow'];

for ($i = 0; $i < count($colors); $i++) {
    echo "Color $i: $colors[$i]\n";
}

// Output:
// Color 0: Red
// Color 1: Green
// Color 2: Blue
// Color 3: Yellow

Example: Numbered List

$tasks = ['Read chapter 5', 'Complete assignment', 'Study for quiz'];

for ($i = 0; $i < count($tasks); $i++) {
    echo ($i + 1) . ". $tasks[$i]\n";
}
// Output: 1. Read chapter 5 ...

3. The `while` Loop

Continues while a condition is true—useful when iteration count is unknown.

$numbers = [1, 2, 3, 4, 5];
$index = 0;

while ($index < count($numbers)) {
    echo $numbers[$index] . "\n";
    $index++;
}

4. The `do-while` Loop

Executes at least once since the condition is checked after the first iteration.

$index = 0;
$fruits = ['Apple', 'Banana'];

do {
    echo $fruits[$index] . "\n";
    $index++;
} while ($index < count($fruits));

Multi-Dimensional Arrays

Use nested loops to process arrays within arrays.

Example: Student Grades

$students = [
    'Alice' => [
        'Math' => 95,
        'English' => 88,
        'Science' => 92
    ],
    'Bob' => [
        'Math' => 78,
        'English' => 85,
        'Science' => 80
    ],
    'Charlie' => [
        'Math' => 90,
        'English' => 92,
        'Science' => 88
    ]
];

foreach ($students as $name => $grades) {
    echo "$name's Grades:\n";

    $total = 0;
    $count = 0;

    foreach ($grades as $subject => $score) {
        echo "  $subject: $score\n";
        $total += $score;
        $count++;
    }

    $average = $total / $count;
    echo "  Average: " . number_format($average, 2) . "\n\n";
}

Loop Control Statements

`break`

Exits the loop immediately when a condition is met:

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

foreach ($numbers as $num) {
    if ($num > 5) {
        break; // Stop when we reach a number greater than 5
    }
    echo $num . " ";
}
// Output: 1 2 3 4 5

`continue`

Skips the current iteration and moves to the next:

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

foreach ($numbers as $num) {
    if ($num % 2 == 0) {
        continue; // Skip even numbers
    }
    echo $num . " ";
}
// Output: 1 3 5 7 9

Common Array Operations

Filtering

$scores = [45, 78, 92, 65, 88, 34, 95];
$passing_scores = [];

foreach ($scores as $score) {
    if ($score >= 60) {
        $passing_scores[] = $score;
    }
}

print_r($passing_scores);
// Output: [78, 92, 65, 88, 95]

Transformation

$prices = [10, 20, 30, 40, 50];
$discounted_prices = [];

foreach ($prices as $price) {
    $discounted_prices[] = $price * 0.8; // 20% discount
}

print_r($discounted_prices);
// Output: [8, 16, 24, 32, 40]

Finding Min/Max

$temperatures = [72, 68, 75, 80, 65, 70];
$max_temp = $temperatures[0];
$min_temp = $temperatures[0];

foreach ($temperatures as $temp) {
    if ($temp > $max_temp) {
        $max_temp = $temp;
    }
    if ($temp < $min_temp) {
        $min_temp = $temp;
    }
}

echo "Highest: $max_temp°F\n";
echo "Lowest: $min_temp°F\n";

Searching

$products = [
    ['id' => 1, 'name' => 'Laptop', 'price' => 999],
    ['id' => 2, 'name' => 'Mouse', 'price' => 25],
    ['id' => 3, 'name' => 'Keyboard', 'price' => 75]
];

$search_id = 2;
$found = null;

foreach ($products as $product) {
    if ($product['id'] == $search_id) {
        $found = $product;
        break;
    }
}

if ($found) {
    echo "Found: {$found['name']} - $" . $found['price'];
}

Best Practices

Choose the right loop: Use foreach without index needs, for when you need indices.
Don’t modify arrays during iteration: Avoid adding/removing elements while looping.
Use descriptive variable names: Prefer $student over $i in foreach loops.
Cache count() in for loops: Calling count() every iteration is inefficient.

// Less efficient
for ($i = 0; $i < count($array); $i++) { }

// Better
$length = count($array);
for ($i = 0; $i < $length; $i++) { }

Prevent infinite loops: Always ensure your loop condition can become false.

// BAD - Infinite loop
while ($i < 10) {
    echo $i;  // Forgot to increment!
}

// GOOD
while ($i < 10) {
    echo $i;
    $i++;
}