Why don't you add the class directly in the HTML? Depending on the page you are in, you can add the active class to the correct link and you wouldn't need to use any scripts.
Edit: I've just realized that maybe you want to use GET requests, but it doesn't look like you are having any parameters in your URL.
You code has some syntax errors, by the way:
$current = array(1 => '', 2 => 'two', 3 => 'three', 4 => 'four');
And some others, like unbalanced parentheses.
Maybe it's better if you tell us what you are trying to accomplish here with your code, so that it's easier for us to help you.