Date fromat change using string format in asp.net

  int strlen;
            string dd, mm, yy, From, To;
            strlen = FromDate.Text.Length;
            dd = FromDate.Text.Substring(0, strlen - 8);
            mm = FromDate.Text.Substring(3, strlen - 8);
            yy = FromDate.Text.Substring(6, strlen - 6);
            From = yy + mm + dd;
            dd = ToDate.Text.Substring(0, strlen - 8);
            mm = ToDate.Text.Substring(3, strlen - 8);
            yy = ToDate.Text.Substring(6, strlen - 6);
            To = yy + mm + dd;