php uncongruence (or config?)

        Hi,

        I am confused as to how to solve this simple problem. Although it seems as some little config issue i am missing.
        I have a file index.php with some html tables and this php code:

        ..html stuff here...
        <?
        print $mod;
        ?>
        ..some more html here...

        If i feed the script with "index.php?mod=2", etc. and run it locally, i get an error saying:

        Notice: Undefined variable: mod in c:\win2kapp\easyphp1-8\www\index.php on line 36

        If i run it on a web server, it works perfectly.
        Whats the difference or where might be the problem in the php.ini? (if its there)
        The server i am using is easyphp, that package that install apache, php and mysql all together. I am running a windows xp box.

        Thanks in advance.

        Pag