Decisions & Control Flow

What you'll learn

Control flow turns facts into behavior. You'll build readable branches, exit invalid paths early, and use PHP's match expression when one value maps to one result.

• Write boolean expressions and if/elseif/else branches
• Reduce nesting with guard clauses
• Use ternary and null coalescing sparingly
• Choose between switch and match
• Avoid assignment and loose-comparison bugs

Turn business rules into boolean decisions

<?php

$age = 22;
$hasTicket = true;

if ($age < 18) {
    echo 'Adult ticket required.';
} elseif (!$hasTicket) {
    echo 'Please buy a ticket.';
} else {
    echo 'Welcome in!';
}

Conditions are evaluated from top to bottom, and only the first matching branch runs. Prefer direct boolean names such as $hasTicket; they make conditions read like sentences.

Guard clauses keep the happy path visible

A guard clause handles an invalid or exceptional case immediately. This prevents a pyramid of nested conditions.

<?php

function discountFor(float $subtotal, bool $isMember): float
{
    if ($subtotal <= 0) {
        return 0.0;
    }

    if (!$isMember) {
        return 0.0;
    }

    return $subtotal >= 100 ? $subtotal * 0.15 : $subtotal * 0.05;
}

echo discountFor(120, true);

Ternary and null coalescing

<?php

$isActive = true;
$nickname = null;

$stateLabel = $isActive ? 'Active' : 'Inactive';
$displayName = $nickname ?? 'Anonymous';

echo "{$displayName}: {$stateLabel}";

Use ternary for one small choice between two expressions. Use ?? specifically for a missing or null value. If a compact expression needs nesting, promote it to a named if block.

Choose switch or match

switch is a statement with fall-through behavior unless you break. match is an expression: it returns a value, compares strictly, and does not fall through.

<?php

$statusCode = 201;

$message = match ($statusCode) {
    200 => 'OK',
    201 => 'Created',
    400 => 'Bad Request',
    404 => 'Not Found',
    default => 'Unknown Status',
};

echo $message;

Common branching mistakes

• Writing if ($status = "paid") assigns instead of compares
• Using loose comparison before normalizing input
• Checking broad conditions before specific ones, making later branches unreachable
• Nesting ternary expressions until business rules become unreadable
• Forgetting default when unmatched input is possible

Recap & quick check