error while round the value?

Question

the following error occured while round the value ("Index was outside the bounds of the array.")

my code behind is..

 double present = Convert.ToDouble(upnoodP.Text);
                double X = 100;
                double totaldays = Convert.ToDouble(uptwd.Text);
                double total = (present * X) / totaldays;
                string[] str = total.ToString().Split('.');
                double no1 = Convert.ToDouble("0." + str[1]);
                double result;
                if (no1 < 0.51)
                {
                    result = Math.Floor(total);
                    uppercent.Text = Convert.ToString(result) + "%";
                }
                else
                {
                    result = Math.Round(total);
                    uppercent.Text = Convert.ToString(result) + "%";
                }

how to resolve this error...