Question

how would I write an IF statement that says if $req does not blank and equals string that does not exist then load, load_template(tpl_path.'err404.tpl'); so if $req does not match or equal something that is valid then show error page.

if ($req == '')              load_template(tpl_path.'index.tpl');
if ($req == 'dologin')      include 'includes/dologin.php';

Answer 1

Use a switch statement:

switch($req) {
  case '':
    load_template(tpl_path.'index.tpl');
    break;
  case 'dologin':
    include 'includes/dologin.php';
    break;
  default:
    load_template(tpl_path.'err404.tpl');
}