这段最简单的API代码为什么没有出现窗口？

请问哪错了？代码可以执行，却没有出现窗口？#include <windows.h>LRESULT CALLBACK WndProc(HWND,UINT,WPARAM,LPARAM);int WINAPI WinMain(HINSTANCE hInstance,
   HINSTANCE hPrevInstance,
   PSTR IpCmdLine,
   int iCmdShow)
{
static TCHAR szAppName[]=TEXT("Hello World");
WNDCLASS wndclass;
HWND hwnd;
MSG msg;
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=NULL;
wndclass.lpszClassName=szAppName;

hwnd=CreateWindow(szAppName,
TEXT("test"),
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)
{
switch(message)
{
case WM_CREATE:
return 0;
case WM_PAINT:
return 0;
case WM_DESTROY:
PostQuitMessage(0);
}
return DefWindowProc(hwnd,message,wParam,lParam);
}