For date calculations you will need to use one of the UDFs found here on the forums... I use serialdate for all things like this.

Serialdate -
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=82573

How to use UDFs -
http://www.kixtart.org/forums/ubbthreads.php?ubb=showflat&Number=81943#Post81943

The rest of the UDFs are here -
http://www.kixtart.org/forums/ubbthreads.php?ubb=postlist&Board=7&page=1

For your code it would be something like
 Code:
IF serialdate($fdate) > serialdate($cdate)