CenterWindow in WIN32

BOOL CenterWindow(HWND hwndWindow)
{
     HWND hwndParent;
     RECT rectWindow, rectParent;

     // make the window relative to its parent
     if ((hwndParent = GetParent(hwndWindow)) != NULL)
     {
         GetWindowRect(hwndWindow, &rectWindow);
         GetWindowRect(hwndParent, &rectParent);

         int nWidth = rectWindow.right - rectWindow.left;
         int nHeight = rectWindow.bottom - rectWindow.top;

         int nX = ((rectParent.right - rectParent.left) - nWidth) / 2 + rectParent.left;
         int nY = ((rectParent.bottom - rectParent.top) - nHeight) / 2 + rectParent.top;

         int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
         int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);

         // make sure that the dialog box never moves outside of the screen
         if (nX < 0) nX = 0;
         if (nY < 0) nY = 0;
         if (nX + nWidth > nScreenWidth) nX = nScreenWidth - nWidth;
         if (nY + nHeight > nScreenHeight) nY = nScreenHeight - nHeight;

         MoveWindow(hwndWindow, nX, nY, nWidth, nHeight, FALSE);

         return TRUE;
     }

     return FALSE;
}