Why I am having error Call to undefined function get_header()?

You get undefined function because you are pointing to the result.php directly. That way WordPress just doesn’t load.

If you need to include result.php in a specific place use get_template_part or even better locate_template

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)