Basicly, I want to write a C++ program and with it, pass messages to a program .exe. This program .exe will run in background and it is going to receive commands from my c++ program. Please, if someone knows a way to do it, that would be awesome.
Use any IPC supported by your OS.
I,m not able to give you a precise answer since I've never worked on windows, but I think what you are looking for is IPC or "Interprocess communication".