days_left = 30;
date_installed = Application.LoadValue("My Application", "Date Installed");
date_installed = String.ToNumber(date_installed);
times_limit = 30;
if date_installed == 0 then
    Application.SaveValue("My Application", "Date Installed", System.GetDate(DATE_FMT_JULIAN));
else
    day_left = (date_installed + times_limit) - System.GetDate(DATE_FMT_JULIAN);
end
if day_left < 1 then
    Dialog.Message("trial period over", "This software has expered");
    Application.Exit();
else
    Dialog.Message("Trial Period", "You have "..days_left.." days in your trial period");
end