windows程序设计制定系统菜单，为什么运行后的窗口不显示。
#include <windows.h>
#define IDM_SYS_ABOUT 1
#define IDM_SYS_HELP 2
#define IDM_SYS_REMOVE 3
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM) ;
static TCHAR szAppName[] = TEXT("PoorMenu") ;
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PSTR szCmdLine, int iCmdShow)
{
HMENU hMenu;
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("The Poor-Person's Menu"),
WS_OVERLAPPEDWINDOW,
CW_USEDEFAULT, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT,
NULL, NULL, hInstance, NULL) ;
hMenu= GetSystemMenu(hwnd, FALSE) ; //得到一个系统菜单的句柄
AppendMenu(hMenu, MF_SEPARATOR, 0, NULL) ; //添加分隔条
AppendMenu(hMenu, MF_STRING, IDM_SYS_ABOUT, TEXT("About...")) ;
AppendMenu(hMenu, MF_STRING, IDM_SYS_HELP, TEXT("Help...")) ;
AppendMenu(hMenu, MF_STRING, IDM_SYS_REMOVE, TEXT("Remove Additions")) ;
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)
{
switch (message) {
case WM_SYSCOMMAND:
switch (LOWORD(wParam)) {
case IDM_SYS_ABOUT:
MessageBox( hwnd, TEXT("A Poor-Person's Menu Program\n")
TEXT("(c) Charles Petzold, 1998"),
szAppName, MB_OK| MB_ICONINFORMATION) ;
return 0 ;
case IDM_SYS_HELP:
MessageBox( hwnd, TEXT("Help not yet implemented!"),
szAppName, MB_OK| MB_ICONEXCLAMATION) ;

return 0 ;
case IDM_SYS_REMOVE:
GetSystemMenu(hwnd, TRUE) ;
return 0 ;
}
break ;
case WM_DESTROY:
PostQuitMessage(0) ;
return 0 ;
}
return DefWindowProc(hwnd, message, wParam, lParam) ;
}

#include <windows.h>
#define IDM_SYS_ABOUT 1
#define IDM_SYS_HELP 2
#define IDM_SYS_REMOVE 3
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
static TCHAR szAppName[] = TEXT("PoorMenu");
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
PSTR szCmdLine, int iCmdShow)
{
HMENU hMenu;
HWND hwnd;
MSG msg;
WNDCLASS wndclass;
wndclass.style = CS_HREDRAW 
[解决办法]
 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("The Poor-Person's Menu"),
WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT,
CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);
hMenu = GetSystemMenu(hwnd, FALSE);
AppendMenu(hMenu, MF_SEPARATOR, 0, NULL);
AppendMenu(hMenu, MF_STRING, IDM_SYS_ABOUT, TEXT("About..."));
AppendMenu(hMenu, MF_STRING, IDM_SYS_HELP, TEXT("Help..."));
AppendMenu(hMenu, MF_STRING, IDM_SYS_REMOVE, TEXT("Remove Additions"));
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)
{
switch (message) {
case WM_SYSCOMMAND:
switch (LOWORD(wParam)) {
case IDM_SYS_ABOUT:
MessageBox(hwnd, TEXT("A Poor-Person's Menu Program\n")
TEXT("(c) Charles Petzold, 1998"),
szAppName, MB_OK 
[解决办法]
 MB_ICONINFORMATION);
return 0;
case IDM_SYS_HELP:
MessageBox(hwnd, TEXT("Help not yet implemented!"),
szAppName, MB_OK 
[解决办法]
 MB_ICONEXCLAMATION);
return 0;
case IDM_SYS_REMOVE:
GetSystemMenu(hwnd, TRUE);
return 0;
}
break;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd, message, wParam, lParam);
}