Warum stellt mein Anmeldeformular keine Verbindung zu meiner MySQL-Datenbank her?

<code class="php">// Replace previous code with the following:

session_start();

if (isset($_SESSION['userid'])) {
    // Redirect to safe page
}

if (isset($_POST['register'])) {
    $email = $_POST['email'];
    $password = $_POST['password']; // Cleartext password from user

    // New code for password hashing
    $hashed_password = password_hash($password, PASSWORD_DEFAULT);

    // Database connection and query
    $host = "localhost";
    $dbname = "database_name";
    $user = "username";
    $pass = "password";

    try {
        $conn = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
        
        $stmt = $conn->prepare("INSERT INTO user_accounts (email, password) VALUES (?, ?)");
        $stmt->execute([$email, $hashed_password]);
        
        // Redirect to login page
        
        $conn = null;
    } catch (PDOException $e) {
        throw $e;
    }
}</code>

<code class="php">// Replace previous code with the following:

session_start();

if (isset($_SESSION['userid'])) {
    // Redirect to safe page
}

if (isset($_POST['login'])) {
    $email = $_POST['email'];
    $password = $_POST['password']; // Cleartext password from user

    // Database connection and query
    $host = "localhost";
    $dbname = "database_name";
    $user = "username";
    $pass = "password";

    try {
        $conn = new PDO("mysql:host=$host;dbname=$dbname", $user, $pass);
        $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        // Get hashed password from database
        $stmt = $conn->prepare("SELECT password FROM user_accounts WHERE email = ?");
        $stmt->execute([$email]);
        $hashed_db_password = $stmt->fetchColumn();

        if (password_verify($password, $hashed_db_password)) {
            // User authenticated successfully
            $_SESSION['userid'] = true;
            
            // Redirect to safe page
        } else {
            // Authentication failed
        }
        
        $conn = null;
    } catch (PDOException $e) {
        throw $e;
    }
}</code>