if ($num < 1) http_response_code(400); die(json_encode(['error' => 'Quantity must be at least 1']));

// If product already in cart, update quantity (add to existing) if (isset($_SESSION['cart'][$product_id])) $new_quantity = $_SESSION['cart'][$product_id]['quantity'] + $num;

// Generate token in main page $_SESSION['csrf_token'] = bin2hex(random_bytes(32)); // In add_to_cart.php if (!hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'] ?? '')) die(json_encode(['error' => 'CSRF validation failed']));

This uses FILTER_VALIDATE_INT (not intval() ), which distinguishes between 0 , null , and false . It rejects decimals, strings, and empty values explicitly. 2.2. Checking Inventory Before Adding A premium addcartphp script never assumes stock. It queries the database live.

// Optionally enforce precision $num = round($num, 2); // e.g., 1.25 kg Protect your server from rapid addcartphp spam:

// Initialize cart session array if not exists if (!isset($_SESSION['cart'])) $_SESSION['cart'] = [];

Searching for addcartphp num high quality suggests you are not looking for a quick, insecure snippet. You want a robust, validated, and scalable solution. This article provides exactly that.

// Re-check stock against new total if ($new_quantity > $product['stock_quantity']) die(json_encode(['error' => 'Cannot add. Total would exceed stock.']));