Warning: mysqli_connect(): (HY000/1045): Access denied for user 'root'@'localhost' (using password: YES) in /opt/lampp/htdocs/demos/oop/include/config.php on line 10

Fatal error: Uncaught Error: Call to undefined function mysql_error() in /opt/lampp/htdocs/demos/oop/include/config.php:10 Stack trace: #0 /opt/lampp/htdocs/demos/oop/include/functions.php(10): DB_Class->__construct() #1 /opt/lampp/htdocs/demos/oop/login.php(4): User->__construct() #2 {main} thrown in /opt/lampp/htdocs/demos/oop/include/config.php on line 10