Warning: Undefined variable $conn in C:\xampp\htdocs\New folder (2)\campuses.php on line 6

Fatal error: Uncaught TypeError: mysqli_query(): Argument #1 ($mysql) must be of type mysqli, null given in C:\xampp\htdocs\New folder (2)\campuses.php:6 Stack trace: #0 C:\xampp\htdocs\New folder (2)\campuses.php(6): mysqli_query(NULL, 'SELECT * FROM c...') #1 C:\xampp\htdocs\New folder (2)\index.php(68): include('C:\\xampp\\htdocs...') #2 {main} thrown in C:\xampp\htdocs\New folder (2)\campuses.php on line 6