How do I convert date in integer format to DateTime without using DateTime?

I have tried:
Code:
Regex regex = new Regex(@"^(0[1-9]|1[012])(0[0-9]|1[0-9]|2[0-9]|3[01])(1[789]|[2-9][0-9])\d\d+$");
if (regex.IsMatch(txt_fromdate.Text) == true)
            {
                DateTime dt = DateTime.ParseExact(txt_fromdate.Text, "MMddyyyy", null);
            }