如果GridView中没有行，则sum将为零。你需要添加一个正确的行数检查，如果没有，则采取不同的行动。



另外......

If there are no rows in the GridView then sum will be zero. You need to add a proper check for the number of rows and take a different action if there are none.

Also ...

        totPenTxt.Text = Convert.ToInt32(0).ToString();
// why not just:
        totPenTxt.Text = "0";