Sevice.cpp Vs Controller.cpp

[wanher3]

Hello all, i have already searched online but can't seem to find a good solid answer to this concept that's bugging me. The concept of writing a Service versus writing a controller. First, what is the definition of the two? how are they used? when should one be writing a service rather than a controller (vice-verse). Any good material and books out there that talks about this? This goes along with App Vs. Lib also. This one maybe silly to ask but on jobs, i have seen project folders been called for example "ExampleApp.cpp" and others "ExampleLib.cpp" and i am not sure how these decisions are made. Thanks