The WM_QUIT message indicates a request to terminate an application and is generated when the application calls the PostQuitMessage function. It causes the GetMessage function to return zero.
WM_QUIT
nExitCode = (int) wParam; // exit code
This message does not have a return value, because it causes the message loop to terminate before the message is sent to the application's window procedure.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winuser.h.
Windows Overview, Window Messages, GetMessage, PostQuitMessage