PHP — OOP

for loop

Execute code a known number of times:

<?php
for ($i = 0; $i < 5; $i++) {
    echo "Iteration $i\n";
}
// 0 1 2 3 4
?>

The for loop has three parts: initialization, condition, and increment. Each part can be empty:

<?php
// Infinite loop (use break to exit)
for (;;) {
    break; // Stops immediately
}
?>

while loop

Repeat while a condition remains true:

<?php
$count = 0;
while ($count < 5) {
    echo "Count: $count\n";
    $count++;
}
// 0 1 2 3 4
?>

The condition is checked before each iteration. If the condition is false from the start, the body never executes:

<?php
$x = 10;
while ($x < 5) {
    echo "This never prints";
}
?>

do-while loop

Execute the body first, then check the condition:

<?php
$count = 0;
do {
    echo "Count: $count\n";
    $count++;
} while ($count < 5);
// 0 1 2 3 4
?>

The body always executes at least once, even if the condition is false:

<?php
$number = 100;
do {
    echo "This prints once\n";
} while ($number < 5);
// Prints once despite the condition being false
?>

foreach loop

Iterate over arrays and iterables:

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

// Iterate values
foreach ($fruits as $fruit) {
    echo "$fruit\n";
}

// Iterate with keys
$person = ["name" => "Alice", "age" => 30, "city" => "NYC"];
foreach ($person as $key => $value) {
    echo "$key: $value\n";
}
?>

Modifying arrays with foreach

By default, foreach works on a copy of the array. Use & to modify the original:

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

// This doesn't modify $numbers
foreach ($numbers as $num) {
    $num = $num * 2;
}
print_r($numbers); // [1, 2, 3, 4, 5]

// This does modify $numbers
foreach ($numbers as &$num) {
    $num = $num * 2;
}
unset($num); // Break the reference
print_r($numbers); // [2, 4, 6, 8, 10]
?>

break and continue

Control loop execution:

<?php
// break: exit the loop entirely
for ($i = 0; $i < 100; $i++) {
    if ($i == 5) {
        break; // Stop at 5
    }
    echo "$i ";
}
// 0 1 2 3 4

// continue: skip to the next iteration
for ($i = 0; $i < 10; $i++) {
    if ($i % 2 == 0) {
        continue; // Skip even numbers
    }
    echo "$i ";
}
// 1 3 5 7 9
?>

Nested loops

Loops inside loops for multi-dimensional data:

<?php
// Multiplication table
for ($i = 1; $i <= 5; $i++) {
    for ($j = 1; $j <= 5; $j++) {
        echo str_pad($i * $j, 4);
    }
    echo "\n";
}
// 1   2   3   4   5
// 2   4   6   8   10
// 3   6   9   12  15
// 4   8   12  16  20
// 5   10  15  20  25
?>

Loop performance

Choose the right loop for your use case:

<?php
$largeArray = range(1, 1000000);

// foreach is faster for arrays (optimized internally)
$start = microtime(true);
foreach ($largeArray as $val) { /* ... */ }
$end = microtime(true);
echo "foreach: " . round(($end - $start) * 1000, 2) . "ms\n";

// for is faster for numeric sequences
$start = microtime(true);
for ($i = 0, $len = count($largeArray); $i < $len; $i++) { /* ... */ }
$end = microtime(true);
echo "for: " . round(($end - $start) * 1000, 2) . "ms\n";
?>

Common patterns

<?php
// Iterate with index
$colors = ["red", "green", "blue"];
for ($i = 0; $i < count($colors); $i++) {
    echo "$i: $colors[$i]\n";
}

// Filter array
$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$evens = [];
foreach ($numbers as $num) {
    if ($num % 2 == 0) {
        $evens[] = $num;
    }
}
print_r($evens); // [2, 4, 6, 8, 10]

// Search array
$search = "banana";
$fruits = ["apple", "banana", "cherry"];
$found = false;
foreach ($fruits as $index => $fruit) {
    if ($fruit === $search) {
        $found = true;
        echo "Found at index $index\n";
        break;
    }
}
?>

Mini Practice

Write PHP code that:

1. Uses a for loop to print numbers 1-20
2. Uses a while loop to find the first number divisible by 7 greater than 50
3. Uses foreach to iterate over an associative array of product prices
4. Uses nested loops to iterate over a 2D array

Up Next

In the next lesson, you'll learn about Arrays — creating, accessing, and manipulating arrays.