Control Flow

Control flow is how PHP decides which lines run, how many times they run, and when the script should stop doing one thing and move to another. Without control flow, a PHP file would only run from top to bottom once.

You use control flow whenever you validate input, choose a shipping rule, loop over orders, skip invalid rows, stop after finding a match, or show different output for different states. It is one of the first places bugs appear because a condition that looks small can change the whole path through the program.

if, elseif, And else

Use if when code should run only when a condition is true. Use elseif for additional branches, and else for the fallback.

<?php

$orderStatus = 'paid';

if ($orderStatus === 'paid') {
    echo "Ship the order\n";
} elseif ($orderStatus === 'pending') {
    echo "Wait for payment\n";
} else {
    echo "Ask support to review\n";
}

// Prints:
// Ship the order

Each branch should represent a real rule. If the words in the condition are unclear, name the condition before the if.

<?php

$totalCents = 7200;
$country = 'GB';

$qualifiesForFreeShipping = $totalCents >= 5000 && $country === 'GB';

if ($qualifiesForFreeShipping) {
    echo "Free shipping\n";
}

// Prints:
// Free shipping

The named variable makes the business rule easier to review than a long condition hidden inside the if.

Guard Clauses

A guard clause handles a case early so the main path stays clear. This is common in validation and permission checks.

<?php

$quantity = 0;

if ($quantity <= 0) {
    echo "Quantity must be at least 1\n";
    return;
}

echo "Quantity accepted\n";

// Prints:
// Quantity must be at least 1

The return stops the rest of the current file or function from running. Later, inside functions, guard clauses become one of the cleanest ways to reject invalid input before doing useful work.

match For Exact Choices

match is useful when one expression maps to one result. It uses strict comparison and returns a value.

<?php

$paymentStatus = 'failed';

$message = match ($paymentStatus) {
    'paid' => 'Ship the order',
    'pending' => 'Wait for payment',
    'failed' => 'Ask the customer to try again',
    default => 'Ask support to review',
};

echo $message . "\n";

// Prints:
// Ask the customer to try again

Use match for clear exact cases. Use if when each branch needs several checks or several statements.

Looping With foreach

foreach is the loop you will use most often with arrays. It runs once for each item.

<?php

$orders = [
    ['id' => 101, 'status' => 'paid'],
    ['id' => 102, 'status' => 'pending'],
    ['id' => 103, 'status' => 'paid'],
];

foreach ($orders as $order) {
    if ($order['status'] !== 'paid') {
        continue;
    }

    echo "Ship order {$order['id']}\n";
}

// Prints:
// Ship order 101
// Ship order 103

continue skips the rest of the current loop item and moves to the next one. Here it skips orders that are not paid.

break Stops A Loop

Use break when the loop has found what it needs and should stop.

<?php

$emails = [
    'bad-address',
    'admin@example.com',
    'support@example.com',
];

$firstValidEmail = null;

foreach ($emails as $email) {
    if (!str_contains($email, '@')) {
        continue;
    }

    $firstValidEmail = $email;
    break;
}

echo $firstValidEmail . "\n";

// Prints:
// admin@example.com

break is useful for searches. Do not keep looping once the answer is already known.

while And for

Use while when a loop should continue while a condition remains true. Use for when you have a simple counter.

<?php

$attemptsRemaining = 3;

while ($attemptsRemaining > 0) {
    echo "Trying request, attempts left: {$attemptsRemaining}\n";
    $attemptsRemaining--;
}

// Prints:
// Trying request, attempts left: 3
// Trying request, attempts left: 2
// Trying request, attempts left: 1

Be careful with while: the condition must eventually become false. Otherwise, the loop can run forever.

<?php

for ($page = 1; $page <= 3; $page++) {
    echo "Fetch page {$page}\n";
}

// Prints:
// Fetch page 1
// Fetch page 2
// Fetch page 3

for is good for counters, but foreach is usually clearer when looping over arrays.

Common Mistakes

The most common mistake is writing the condition backwards. Read conditions out loud: "if status is not paid, continue" is easier to check than guessing from symbols alone.

Another common mistake is forgetting the fallback branch. If a status can be paid, pending, failed, or unknown, the code should say what happens when the value is unknown.

Be careful with loops that change the array they are looping over. That can be useful later, but for beginner code it is usually clearer to build a new array or print the result directly.

What You Should Be Able To Do

After this lesson, you should be able to:

• choose between if, elseif, else, and match;
• write a guard clause for invalid input;
• loop over arrays with foreach;
• use continue to skip one item;
• use break to stop after finding a result;
• use while and for for simple repeated work;
• explain which branch or loop iteration will run before executing the code.