In what ways can separating form input handling from session variable management improve the reliability and consistency of PHP scripts in a multi-page web application?

Separating form input handling from session variable management can improve the reliability and consistency of PHP scripts in a multi-page web application by ensuring that each component has a clear and distinct responsibility. This separation allows for better organization of code, easier debugging, and reduces the likelihood of errors caused by mixing concerns. By keeping form input handling and session variable management separate, it becomes easier to maintain and scale the application.

// Form input handling
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Process form data
    $username = $_POST['username'];
    $password = $_POST['password'];
    
    // Validate input data
    // Perform necessary actions
}

// Session variable management
session_start();

if (isset($_SESSION['user_id'])) {
    // User is logged in, perform necessary actions
} else {
    // User is not logged in, redirect or display login form
}