try
{
    int num = Convert.ToInt32("");  //這一行會報錯
}catch(Exception ex)
{
    MessageBox.Show(ex.StackTrace);
}

try
{
    int num = Convert.ToInt32("");
}catch(Exception ex)
{
    MessageBox.Show(ex.StackTrace.Substring(ex.StackTrace.IndexOf("行號"), ex.StackTrace.Length - ex.StackTrace.IndexOf("行號")));
}