VC++ DialogBox의 윈도우 옮기기

BOOL CALLBACK DialogProc(HWND hWnd, UINT iMsg, WPARAM wParam, LPARAM lParam)
{

      int x, y;
      RECT rect;

      switch (iMsg)
      {
       case WM_INITDIALOG:
             GetClientRect(hWnd, &rect);                                         // 현재 윈도우의 크기 얻기
             x=::GetSystemMetrics(SM_CXSCREEN);                        // 모니터의 가로 전체 크기 얻기
             y=::GetSystemMetrics(SM_CYSCREEN);                        // 모니터의 세로 전체 크기 얻기
             x=(x-rect.right)/2;
             y=(y-rect.bottom)/2;
             MoveWindow(hWnd, x, y, rect.right, rect.bottom, TRUE);  // 윈도우를 옮기는 루틴
             return TRUE;
             break;
       case WM_COMMAND:
             switch(LOWORD(wParam)) {
                   case IDOK:
                         LineIDGen(hWnd);
                         EndDialog(hWnd, IDOK);
                         return TRUE;
                   case IDCANCEL:
                         EndDialog(hWnd, IDCANCEL);
                         return TRUE;
             }
             break;
       case WM_CLOSE:
             EndDialog(hWnd, 0);
             return FALSE;
       default:
             return FALSE;
       }
       return TRUE;
}