Lesson 06 of 20

8 mins read

Loops: While, For & Foreach Traversal

In Plain English

Loops allow automated repetitive execution. Learn while, do-while, for counters, break/continue control, and the powerhouse foreach loop designed specifically for iterating over indexed arrays and key-value hash maps.

The Mental Model

"A for loop is an odometer ticking off exact mile markers from 1 to 10. A foreach loop is an automated postal worker picking up every single letter in a delivery bag one by one until the bag is empty."

Deep Dive: How It Works

The foreach Loop: foreach ($items as $item) or foreach ($map as $key => $val) traverses any iterable.

By-Reference Iteration: foreach ($items as &$val) allows direct modification of elements in place (remember to unset($val) after loop!).

Jump Statements: break stops loop execution; continue skips immediately to the next iteration.

Syntax Blueprint

<?php

foreach ($users as $id => $name) {
    echo "ID: {$id} => {$name}\n";
}

Use foreach with $key => $value syntax to traverse array elements smoothly.

Core Rules to Remember

Foreach Efficiency: foreach is the standard, most idiomatic way to iterate over arrays and iterables in PHP.

Break Levels: PHP supports break 2; and continue 2; to break out of multiple nested loop levels.

Array Copy Behavior: By default, foreach operates on a copy of the array array pointer.

Common Beginner Traps & How to Fix Them

Mistake:Leaving a reference variable bound after a foreach ($arr as &$v) loop.

Why it happens: $v remains bound to the last element of $arr; subsequent assignments to $v will accidentally overwrite the last element.

How to fix: Always call unset($v) immediately following by-reference foreach loops.

Pro Tip: Prefer foreach over for ($i=0; $i<count($arr); $i++) because count() inside the loop header causes O(N^2) evaluation overhead.

Live Interactive Example

Hit Run Code to see it live

Iterating Key-Value Configuration with Foreach

PHP 8.2 / CLI

Output Console

Click "Run Code" to view the rendered output.

How it works: foreach smoothly unpacked both the string keys ($name) and integer values ($port).

Your Turn: Micro Challenge

No pressure! Edit the starter code below and test your solution with instant feedback.

Micro Exercise

Filter Even Numbers with Foreach

Declare an array $numbers = [1, 2, 3, 4, 5, 6].
Iterate using foreach and print each even number on a new line preceded by "Even: ".

Sandbox Output

Click "Run & Check" to test your solution.

Finished reading and practicing?

Mark this lesson as completed to update your course progress.