What are common pitfalls or challenges faced by beginners when integrating HTML/PHP code for interactive features like quizzes and calculations on a website?

One common pitfall for beginners is not properly sanitizing user input, which can lead to security vulnerabilities like SQL injection attacks. To solve this, always validate and sanitize user input before using it in PHP code to prevent malicious input.

$user_input = $_POST['user_input'];
$clean_input = htmlspecialchars(strip_tags($user_input));