PHP Conditionals and Decision Making

Conditionals choose which code runs. The syntax is simple; the important part is expressing business rules clearly and avoiding truthiness surprises.

If, Elseif, and Else

<?php
declare(strict_types=1);

$score = 87;

if ($score >= 90) {
    $grade = 'A';
} elseif ($score >= 80) {
    $grade = 'B';
} elseif ($score >= 70) {
    $grade = 'C';
} else {
    $grade = 'Needs work';
}

echo $grade;

Conditions are evaluated from top to bottom. Put the most specific conditions before broader ones.

Prefer Strict Comparison

<?php
$value = '0';

var_dump($value == false);  // true because of coercion
var_dump($value === false); // false because the types differ

Combining Conditions

<?php
declare(strict_types=1);

$isAuthenticated = true;
$role = 'manager';
$accountActive = true;

if ($isAuthenticated && $accountActive && in_array($role, ['admin', 'manager'], true)) {
    echo 'Access granted.';
}

Use parentheses when an expression mixes && and ||. The small cost in typing is worth the improved readability.

Use Match for Value Mapping

<?php
declare(strict_types=1);

$status = 'past_due';

$message = match ($status) {
    'active' => 'The account is active.',
    'past_due' => 'Payment is required.',
    'suspended' => 'The account is suspended.',
    default => 'The account status is unknown.',
};

echo $message;

match uses strict comparison, returns a value, and does not fall through between branches.

Guard Clauses Reduce Nesting

<?php
declare(strict_types=1);

function cancelTrip(Trip $trip, User $actor): void
{
    if (!$actor->can('trip.cancel')) {
        throw new AuthorizationException('Permission denied.');
    }

    if ($trip->isCompleted()) {
        throw new DomainException('A completed trip cannot be cancelled.');
    }

    if ($trip->isCancelled()) {
        return;
    }

    $trip->cancel($actor->id());
}

Early exits keep the successful path easy to see and make invalid states explicit.

Real-World Example: Quote Approval

<?php
declare(strict_types=1);

function approvalRoute(int $amountCents, bool $hasPricingOverride): string
{
    if ($amountCents < 0) {
        throw new InvalidArgumentException('Amount cannot be negative.');
    }

    return match (true) {
        $hasPricingOverride => 'owner_review',
        $amountCents >= 500_000 => 'manager_review',
        default => 'automatic',
    };
}

Common Mistakes

• Using assignment inside a condition by mistake: if ($status = 'active').
• Comparing unnormalized user input directly to internal values.
• Writing a long chain of role checks instead of a permission policy.
• Using truthiness where 0, '0', an empty array, and null have different meanings.
• Hiding a button without enforcing the same permission on the server.