Chap1Exa1.obj : error LNK2001: unresolved external symbol "long _stdcall WndPro解决思路

#include <windows.h>

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

int APIENTRY WinMain(HINSTANCE hInstance , HINSTANCE hPrevInstance ,
                     LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASS wndclass;
    HWND hwnd;
    MSG msg;
    /****************************/
    wndclass.style = CS_HREDRAW|CS_VREDRAW;
    wndclass.lpfnWndProc = WndPro;
    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 = "Chap1Exa1";
    if(!RegisterClass(&wndclass))
        return FALSE;

    hwnd = CreateWindow("Chap1Exa1","Chap1Exa1",WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,CW_USEDEFAULT,
        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_PAINT:
        HDC hdc;
        PAINTSTRUCT ps;
        hdc = BeginPaint(hwnd,&ps);

        TextOut(hdc,20,60,"The First Windows Application Showing Window",35);
        EndPaint(hwnd,&ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc(hwnd,message,wParam,lParam);
}