看看这个哪里出错了,该怎么处理

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;
    TCHAR szHello[MAX_LOADSTRING];
    static POINT pt[MAXPOINT];
    static int nCount=0;
    int i,j;


    switch (message) 
    {
        case WM_COMMAND:
            wmId    = LOWORD(wParam); 
            wmEvent = HIWORD(wParam); 
            // Parse the menu selections:
            switch (wmId)
            {
                case IDM_ABOUT:
                   DialogBox(hInst, (LPCTSTR)IDD_ABOUTBOX, hWnd, (DLGPROC)About);
                   break;
                case IDM_EXIT:
                   DestroyWindow(hWnd);
                   break;
                default:
                   return DefWindowProc(hWnd, message, wParam, lParam);
            }
            break;
        case WM_LBUTTONDOWN:
            pt[nCount].x=LOWORD(lParam);
            pt[nCount].y=LOWORD(lParam);
            SetPixel(hdc,LOWORD(lParam),HIWORD(lParam),RGB(255,0,0));
            nCount++;
            break;
        case WM_RBUTTONDOWN:
            InvalidateRect(hWnd,NULL,TRUE);
            break;


        case WM_PAINT:
            hdc = BeginPaint(hWnd, &ps);
            // TODO: Add any drawing code here...
            SetCursor(LoadCursor(NULL,IDC_WAIT));
            ShowCursor(TRUE);
            for (i=0;i<nCount-1;i++)
            {
                for (j=i+1;j<nCount;j++)
                {
                    MoveToEx(hdc,pt[i].x,pt[i].y,NULL);
                    LineTo(hdc,pt[j].x,pt[j].y);

                }
            }
            ShowCursor(FALSE);
            SetCursor(LoadCursor(NULL,IDC_ARROW));

            RECT rt;
            GetClientRect(hWnd, &rt);
            
            EndPaint(hWnd, &ps);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hWnd, message, wParam, lParam);
   }
   return 0;
}