The main window in most applications is a top-level frame window. An application creates a top-level frame window by specifying the handle of the desktop window, or HWND_DESKTOP, as the hwndParent parameter in a call to the WinCreateStdWindow function.

The following figure shows the main() function for a simple PM application. This function initializes the application, creates a message queue, and registers the window class for the client window before creating a top-level frame window.

    #define IDR_RESOURCES 1

    MRESULT EXPENTRY ClientWndProc(HWND, ULONG, MPARAM, MPARAM);

    int main(VOID)
    {
        HWND hwndFrame;
        HWND hwndClient;
        HMQ  hmq;
        QMSG qmsg;
        HAB  hab;

        /* Set the frame-window creation flags.                       */
        ULONG flFrameFlags =
            FCF_TITLEBAR      |   /* Title bar                        */
            FCF_SIZEBORDER    |   /* Size border                      */
            FCF_MINMAX        |   /* Minimize and maximize buttons.   */
            FCF_SYSMENU       |   /* System menu                      */
            FCF_SHELLPOSITION |   /* System-default size and position */
            FCF_TASKLIST ;        /* Add name to Task List.           */

        /* Initialize the application for PM                          */
        hab = WinInitialize(0);

        /* Create the application message queue.                      */
        hmq = WinCreateMsgQueue(hab, 0);

        /* Register the class for the client window.                  */
        WinRegisterClass(
            hab,                    /* Anchor block handle            */
            "MyPrivateClass",       /* Name of class being registered */
            (PFNWP)ClientWndProc,   /* Window procedure for class     */
            CS_SIZEREDRAW |         /* Class style                    */
            CS_HITTEST,             /* Class style                    */
            0);                     /* Extra bytes to reserve         */

        /* Create a top-level frame window with a client window       */
        /* that belongs to the window class "MyPrivateClass".         */
        hwndFrame = WinCreateStdWindow(
            HWND_DESKTOP,      /* Parent is desktop window.           */
            WS_VISIBLE,        /* Make frame window visible.          */
            &flFrameFlags,     /* Frame controls                      */
            "MyPrivateClass",  /* Window class for client             */
            NULL,              /* No window title                     */
            WS_VISIBLE,        /* Make client window visible .        */
            (HMODULE) 0,       /* Resources in application module     */
            IDR_RESOURCES,     /* Resource identifier                 */
            NULL);             /* Pointer to client window handle     */

        /* Start the main message loop. Get messages from the         */
        /* queue and dispatch them to the appropriate windows.        */
        while (WinGetMsg(hab, &qmsg, 0, 0, 0))
               WinDispatchMsg(hab, &qmsg);

        /* Main loop has terminated. Destroy all windows and the      */
        /* message queue; then terminate the application.             */
        WinDestroyWindow(hwndFrame);
        WinDestroyMsgQueue(hmq);
        WinTerminate(hab);

        return 0;
    }