windows编程为什么不能在vc++6.0上运行？

#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;
    WNDCLASS wc;
    char lpszClassName[]="my winows!";
    wc.style=0;
    wc.lpszMenuName=NULL;
    wc.lpszClassName=lpszClassName;
    wc.lpfnWndProc=WndProc;
    wc.hInstance=hInstance;
    wc.hIcon=LoadIcon(NULL,IDI_APPLICATION);
    wc.hCursor=LoadCursor(NULL,IDC_ARROW);
    wc.hbrBackground=(HBRUSH)GetStockObject(WHITE_BRUSH);
    wc.cbWndExtra=0;
    wc.cbClsExtra=0;
    RegisterClass(&wc);
    hwnd=CreateWindow(lpszClassName,"windows",WS_OVERLAPPEDWINDOW,120,50,800,600,NULL,NULL,hInstance,NULL);
    ShowWindow(hwnd,nCmdShow);
    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_LBUTTONDOWN:
        MessageBeep(0);
        break;
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hwnd,message,wParam,lParam);
    }
    return 0;
}
LIBCD.lib(crt0.obj) : error LNK2001: unresolved external symbol _main
Debug/a.exe : fatal error LNK1120: 1 unresolved externals
执行 link.exe 时出错.
为什么一个最简单的windows编程在vc++6.0上运行不了？求大神指教.....