PHP Control Flow Explained: if, else, switch and loops for Beginners

<?php

// Imagine this score came from a student's exam result
$studentScore = 74;

// PHP checks this condition first
if ($studentScore >= 90) {
    // This only runs if the score is 90 or above
    $grade = 'A';
    $feedback = 'Excellent work!';

} elseif ($studentScore >= 75) {
    // Only checked if the first condition was false
    $grade = 'B';
    $feedback = 'Good effort, just above average.';

} elseif ($studentScore >= 60) {
    // Only checked if both conditions above were false
    $grade = 'C';
    $feedback = 'Passing, but there is room to grow.';

} elseif ($studentScore >= 40) {
    $grade = 'D';
    $feedback = 'Just scraped through. Review the material.';

} else {
    // This is the safety net — runs only when ALL conditions above are false
    $grade = 'F';
    $feedback = 'Did not meet the passing mark. Please resit.';
}

// Now we use the variables we set inside the conditions
echo "Score: $studentScore" . PHP_EOL;
echo "Grade: $grade" . PHP_EOL;
echo "Feedback: $feedback" . PHP_EOL;

// Let's also demonstrate a simple boolean if/else
$isLoggedIn = true;

if ($isLoggedIn) {
    // true means this block runs
    echo 'Welcome back! Your dashboard is ready.' . PHP_EOL;
} else {
    echo 'Please log in to continue.' . PHP_EOL;
}

<?php

// Simulate a delivery status code coming from a logistics API
$deliveryStatusCode = 'OUT_FOR_DELIVERY';

switch ($deliveryStatusCode) {

    case 'ORDER_PLACED':
        // This runs only if $deliveryStatusCode exactly equals 'ORDER_PLACED'
        $statusMessage = 'Your order has been received and is being processed.';
        $estimatedAction = 'No action needed.';
        break; // CRITICAL: without break, PHP falls through to the next case

    case 'PACKED':
        $statusMessage = 'Your order has been packed and is awaiting pickup.';
        $estimatedAction = 'Should ship within 24 hours.';
        break;

    case 'IN_TRANSIT':
        $statusMessage = 'Your package is on its way.';
        $estimatedAction = 'Track your shipment for live updates.';
        break;

    case 'OUT_FOR_DELIVERY':
        // This case matches our variable, so this block runs
        $statusMessage = 'Your package is out for delivery today!';
        $estimatedAction = 'Stay home — delivery expected by 6 PM.';
        break;

    case 'DELIVERED':
        $statusMessage = 'Your package has been delivered.';
        $estimatedAction = 'Check your delivery location.';
        break;

    case 'FAILED_DELIVERY':
        $statusMessage = 'Delivery attempt failed.';
        $estimatedAction = 'Reschedule your delivery online.';
        break;

    default:
        // Runs if none of the cases above matched
        $statusMessage = 'Unknown status code received.';
        $estimatedAction = 'Contact customer support.';
        break;
}

echo "Status: $deliveryStatusCode" . PHP_EOL;
echo "Message: $statusMessage" . PHP_EOL;
echo "Next Step: $estimatedAction" . PHP_EOL;

// Bonus: Intentional fall-through (a VALID use case)
// If you want two cases to share the same outcome:
$dayOfWeek = 'Saturday';

switch ($dayOfWeek) {
    case 'Saturday':
    case 'Sunday':
        // Both Saturday AND Sunday fall through to this shared output
        echo PHP_EOL . "$dayOfWeek is a weekend — support is limited." . PHP_EOL;
        break;
    default:
        echo PHP_EOL . "$dayOfWeek is a working day — full support available." . PHP_EOL;
        break;
}

<?php

// ─────────────────────────────────────────
// 1. FOR LOOP: Generate a multiplication table
// Use for: when you know the exact number of iterations
// ─────────────────────────────────────────
$multiplyBy = 5;
echo "--- Multiplication Table for $multiplyBy ---" . PHP_EOL;

for ($counter = 1; $counter <= 10; $counter++) {
    // $counter starts at 1, runs while <= 10, adds 1 each iteration
    $result = $multiplyBy * $counter;
    echo "$multiplyBy x $counter = $result" . PHP_EOL;
}

// ─────────────────────────────────────────
// 2. WHILE LOOP: Simulate a countdown timer
// Use while: when repetitions depend on a changing condition
// ─────────────────────────────────────────
echo PHP_EOL . "--- Launch Countdown ---" . PHP_EOL;
$secondsRemaining = 5;

while ($secondsRemaining > 0) {
    // Keep looping as long as secondsRemaining is greater than 0
    echo "T-minus $secondsRemaining seconds..." . PHP_EOL;
    $secondsRemaining--; // decrement by 1 each time — without this, infinite loop!
}
echo 'Liftoff!' . PHP_EOL;

// ─────────────────────────────────────────
// 3. DO...WHILE LOOP: Ask at least once
// Use do-while: when the action must happen before the check
// ─────────────────────────────────────────
echo PHP_EOL . "--- Do-While Demo ---" . PHP_EOL;
$attemptsAllowed = 3;
$attemptsMade = 0;

do {
    // This block runs FIRST, then the condition is checked
    $attemptsMade++;
    echo "Processing attempt $attemptsMade of $attemptsAllowed..." . PHP_EOL;
} while ($attemptsMade < $attemptsAllowed);

echo 'All attempts used.' . PHP_EOL;

// ─────────────────────────────────────────
// 4. FOREACH LOOP: Process a product inventory
// Use foreach: always when iterating over an array
// ─────────────────────────────────────────
echo PHP_EOL . "--- Product Inventory Report ---" . PHP_EOL;

$productInventory = [
    'Wireless Mouse'  => 42,
    'Mechanical Keyboard' => 7,
    'USB-C Hub'       => 0,
    'Monitor Stand'   => 15,
];

foreach ($productInventory as $productName => $stockCount) {
    // $productName gets the KEY, $stockCount gets the VALUE each iteration
    if ($stockCount === 0) {
        echo "$productName: OUT OF STOCK" . PHP_EOL;
    } elseif ($stockCount < 10) {
        echo "$productName: LOW STOCK ($stockCount remaining)" . PHP_EOL;
    } else {
        echo "$productName: In stock ($stockCount units)" . PHP_EOL;
    }
}

<?php

// ─────────────────────────────────────────
// TERNARY OPERATOR
// Syntax: $result = (condition) ? valueIfTrue : valueIfFalse;
// ─────────────────────────────────────────

$cartItemCount = 3;

// The long way with if/else:
// if ($cartItemCount === 1) { $itemLabel = 'item'; } else { $itemLabel = 'items'; }

// The ternary shorthand — much cleaner for simple cases like this:
$itemLabel = ($cartItemCount === 1) ? 'item' : 'items';
echo "You have $cartItemCount $itemLabel in your cart." . PHP_EOL;

// Null coalescing operator ?? — a special ternary for checking null/undefined
// Returns the left side if it exists and is not null, otherwise the right side
$userDisplayName = $_GET['username'] ?? 'Guest';
// Since $_GET['username'] isn't set in CLI, this safely defaults to 'Guest'
echo "Hello, $userDisplayName!" . PHP_EOL;

// ─────────────────────────────────────────
// MATCH EXPRESSION (PHP 8.0+)
// Returns a value, uses strict comparison, no fall-through
// ─────────────────────────────────────────

$httpStatusCode = 404;

// match returns a value directly — we assign it to $statusDescription
$statusDescription = match($httpStatusCode) {
    200 => 'OK — Request succeeded.',
    201 => 'Created — Resource successfully created.',
    301 => 'Moved Permanently — Redirect to new URL.',
    302 => 'Found — Temporary redirect.',
    400 => 'Bad Request — Check your request parameters.',
    401 => 'Unauthorized — Authentication required.',
    403 => 'Forbidden — You do not have permission.',
    404 => 'Not Found — This resource does not exist.',  // This arm matches
    500 => 'Internal Server Error — Something went wrong on the server.',
    default => 'Unknown status code.'
};

echo PHP_EOL . "HTTP $httpStatusCode: $statusDescription" . PHP_EOL;

// match with multiple values per arm (comma-separated)
$currentMonth = 8; // August

$season = match(true) {
    in_array($currentMonth, [12, 1, 2])  => 'Winter',
    in_array($currentMonth, [3, 4, 5])   => 'Spring',
    in_array($currentMonth, [6, 7, 8])   => 'Summer',  // This matches month 8
    in_array($currentMonth, [9, 10, 11]) => 'Autumn',
    default => 'Unknown'
};

echo "Month $currentMonth is in $season." . PHP_EOL;