Remember that he same Window procedure may service several instances of the same Windows class. Each instance will have its own window with a different handle, but they will all go through the same procedure. The relationship between instances of the same program, their windows and the program s Window class and procedure. The message is just a number. Symbolic names for these numbers are defined in windows.h.
Every message is accompanied by two parameters whose meaning depends on the kind of message.
To learn more about window procedure study the help files that come with your compiler. Here s our minimalist implementation of Window procedure. We do it by posting the final quit message. This message will terminate the message loop and control will be returned to WinMain . A lot of Windows APIs take a large number of arguments.