If you want the application to run all the time (in the background) with not user interaction then use Windows Services If you want the user to have interaction with application, then you need to build Windows Applications (Winform, WPF , etc)
Yusuf Oh didn't you notice, analogous to square roots, they recently introduced rectangular, circular, and diamond roots to determine the size of the corresponding shapes when given the area. Luc Pattyn[^]