PostQuitMessage

Synopsis

VOID PostQuitMessage(
    _In_ int nExitCode
);

Parameters

nExitCode	exit code to be returned to the system when the application terminates.

Return Value

This function does not return a value.

Remarks

Posts a WM_QUIT message to the thread's message queue. This causes the GetMessage function to return 0 and initiates the termination of the message loop.

Typical usage:

while (GetMessage(&msg, NULL, 0, 0))
{
    TranslateMessage(&msg);
    DispatchMessage(&msg);
}
return (int)msg.wParam; // or return nExitCode passed to PostQuitMessage

Examples

#include 

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch(msg)
    {
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, msg, wParam, lParam);
}

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrev, LPSTR lpCmd, int nShow)
{
    MSG msg;
    // Register class, create window, etc.
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return (int)msg.wParam;
}

Microsoft Docs