Unlike a traditional application, a Microsoft Windows application does not make explicit function calls (such as to getchar) to obtain input. Instead, it waits for Windows to pass input to the application.
Windows passes all input for an application to the various windows in the application. Each window has a function, called a window procedure, that Windows calls whenever it has input for the window. The window procedure processes the input and returns control to Windows. For more information about window procedures, see Chapter 35, “Window Procedures.”
This chapter describes messages and messages queues and explains how to use them in your application.