Php code in all pages

I need to enter this php code in all the pages, any suggestions?

$memID = $_COOKIE['memberID']; $activo = isProfileActive(); if ($activo){ echo '<link rel="stylesheet" href="templates/base/css/act.css" />'; } else {echo '<link rel="stylesheet" href="templates/base/css/noact.css" />';}

Sounds like you want to change the style sheet based on if the person is active or not.  I don't understand the purpose of this.