WM_QUIT
wExit = wParam; /* exit code */
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.
wExit
Value of wParam. Specifies the exit code given in the PostQuitMessage function.
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.