if( empty($errors)) {
            mysql_query("INSERT INTO students (ID, username, password, email) VALUES('', '$username', '$password', '$email') ") or die(mysql_error());

            foreach ($class as $value) {
                $value = mysql_real_escape_string($value);

                $student_id = mysql_insert_id();
                mysql_query("INSERT INTO enrollments (ID, student_id, course_id) VALUES('', '$student_id', '$value') ") or die(mysql_error());
        }
            mysql_close($con);
            header("Location: login.php");
    }