I have a Generic List. it has a ListfilesToProcess.Count property which returns total number of items, but I want to count certain number of items in list with conditional-s
Yes, use LINQ's Count method, with the overload taking a predicate:
Count
int count = ListFilesToProcess.Count(item => item.IsChecked);
In general, whenever you feel you want to get rid of a loop (or simplify it) - you should look at LINQ.