什么错误

什么错误
--------------------Configuration: createwindow - Win32 Debug--------------------
Linking...
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/createwindow.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.createwindow.exe - 2 error(s), 0 warning(s)
#include "stdafx.h"
#include<windows.h>
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
int WINAPI WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{   HWND hwnd;MSG msg;
    WNDCLASSEX wndclass;
static char appname[]="Hello,world";
wndclass.cbClsExtra=0;
wndclass.cbSize =sizeof(wndclass);
wndclass.cbWndExtra =0;
wndclass.hbrBackground =(HBRUSH)(COLOR_WINDOW+1);
wndclass.hCursor =LoadIcon(NULL,NULL);
wndclass.hIcon =LoadIcon(NULL,NULL);
wndclass.hIconSm =LoadIcon(NULL,NULL);
wndclass.hInstance =hInstance;
wndclass.lpfnWndProc =(WNDPROC)WndProc;
wndclass.lpszClassName =appname;
wndclass.lpszMenuName=NULL;
wndclass.style =CS_HREDRAW | CS_VREDRAW;
RegisterClassEx(&wndclass);
hwnd=CreateWindow(appname,"Hello,world",WS_OVERLAPPEDWINDOW,
      CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, NULL, NULL, hInstance, NULL);
ShowWindow(hwnd, SW_SHOW);
    UpdateWindow(hwnd);
while(GetMessage(&msg,NULL,0,0)){
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam ;
}LRESULT CALLBACK WndProc(HWND hwnd,UINT msg,WPARAM wparam,LPARAM lparam)
{ switch(msg)
{
case WM_PAINT:
        return 0;
case WM_DESTROY:
PostQuitMessage(0);
return 0;
}
return DefWindowProc(hwnd,msg,wparam,lparam);
}