Creating a Trial Version

Hi,

I want to put my C++ windows app online so people can download it and try it out. I want to make this download a trial version, so that after 30 days the user will be forced to enter a code in order to proceed using it. How can I do this?, are there a number of ways? and what do they involve?

Thanks.

I'm not sure how to EXACTLY do it as I never had to use such a method before.... But it would involve setting a timer (WM_TIMER) and/or just save something in registery or some file whatever suits you