Get Input Without Pressing Enter

Question

Guys, I want to get input from the user, but you know if we press some buttons it appears on the screen, the thing that I want is letter to not appear on the screen when we press and some codes are going to be executed according to the button user pressed.

Second thing, I want it to work while user looking to another program. Something like cheat, trainer, keylogger or a game.

(edit: im using c++)