为什么窗口不显示菜单呢？

#include <windows.h>

#include "resource.h"



#define ID_TIMER 1



LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM) ;



TCHAR szAppName[] = TEXT ("MenuDemo") ;



int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,

                    PSTR szCmdLine, int iCmdShow)

{

     HWND     hwnd ;

     MSG      msg ;

     WNDCLASS wndclass ;

     

     wndclass.style         = CS_HREDRAW | CS_VREDRAW ;

     wndclass.lpfnWndProc   = WndProc ;

     wndclass.cbClsExtra    = 0 ;

     wndclass.cbWndExtra    = 0 ;

     wndclass.hInstance     = hInstance ;

     wndclass.hIcon         = LoadIcon (NULL, IDI_APPLICATION) ;

     wndclass.hCursor       = LoadCursor (NULL, IDC_ARROW) ;

     wndclass.hbrBackground = (HBRUSH) GetStockObject (WHITE_BRUSH) ;

     wndclass.lpszMenuName  = szAppName ;

     wndclass.lpszClassName = szAppName ;

     

     if (!RegisterClass (&wndclass))

     {

          MessageBox (NULL, TEXT ("This program requires Windows NT!"),

                      szAppName, MB_ICONERROR) ;

          return 0 ;

     }

     

     hwnd = CreateWindow (szAppName, TEXT ("Menu Demonstration"),

                          WS_OVERLAPPEDWINDOW,

                          CW_USEDEFAULT, CW_USEDEFAULT,

                          CW_USEDEFAULT, CW_USEDEFAULT,

                          NULL, NULL, hInstance, NULL) ;

     

     ShowWindow (hwnd, iCmdShow) ;

     UpdateWindow (hwnd) ;

     

     while (GetMessage (&msg, NULL, 0, 0))

     {

          TranslateMessage (&msg) ;

          DispatchMessage (&msg) ;

     }

     return msg.wParam ;

}



LRESULT CALLBACK WndProc (HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

{

	static int idColor[5] = {WHITE_BRUSH, LTGRAY_BRUSH, GRAY_BRUSH, DKGRAY_BRUSH, BLACK_BRUSH};

	static int iSelection = IDM_BKGND_WHITE;

	HMENU hMenu;



	switch(message)

	{

	case WM_COMMAND:

		hMenu = GetMenu(hwnd);



		switch(LOWORD(wParam))

		{

		case IDM_FILE_NEW:

		case IDM_FILE_OPEN:

		case IDM_FILE_SAVE:

		case IDM_FILE_SAVE_AS:

			MessageBeep (0) ;

			return 0 ;

		case IDM_APP_EXIT:

			SendMessage(hwnd, WM_CLOSE, 0, 0);

			return 0;

		case IDM_EDIT_UNDO:

		case IDM_EDIT_CUT:

		case IDM_EDIT_COPY:

		case IDM_EDIT_PASTE:

		case IDM_EDIT_CLEAR:

			MessageBeep (0) ;

			return 0 ;

		case IDM_BKGND_WHITE:         // Note: Logic below

		case IDM_BKGND_LTGRAY:        //   assumes that IDM_WHITE

		case IDM_BKGND_GRAY:          //   through IDM_BLACK are

		case IDM_BKGND_DKGRAY:        //   consecutive numbers in

		case IDM_BKGND_BLACK:   



			CheckMenuItem(hMenu, iSelection, MF_UNCHECKED);

			iSelection = LOWORD(wParam);

			CheckMenuItem(hMenu, iSelection, MF_CHECKED);



			SetClassLong(hwnd,GCL_HBRBACKGROUND, (LONG) GetStockObject(idColor[LOWORD(wParam)] - IDM_BKGND_WHITE));



			InvalidateRect(hwnd, NULL, TRUE);

		case IDM_TIMER_START:

			if (SetTimer(hwnd, ID_TIMER, 1000, NULL))

			{

				EnableMenuItem(hMenu, IDM_TIMER_START, MF_GRAYED);

				EnableMenuItem(hMenu, IDM_TIMER_STOP, MF_ENABLED);

			}

			return 0;

		case IDM_TIMER_STOP:

			KillTimer(hwnd, ID_TIMER);

			EnableMenuItem(hMenu, IDM_TIMER_START, MF_ENABLED);

			EnableMenuItem(hMenu, IDM_TIMER_STOP, MF_GRAYED);

			return 0;

		case IDM_APP_HELP:

			MessageBox(hwnd, TEXT("Help not yet implemented!"), 

				       szAppName, MB_ICONINFORMATION | MB_OK);

			return 0;

		}

		break;

	case WM_TIMER:

		MessageBeep(0);

		return 0;

	case WM_DESTROY:

		PostQuitMessage(0);

		return 0;

	}

	return DefWindowProc(hwnd, message, wParam, lParam);



	

}