C# ID card verification small example

 private string CheckCidInfo(string cid)
            double iSum = 0;
            rg = new (@"^\d{17}(\d|x)$");
            mc = (cid);
            if (!)
            {
                return "";
            }
            cid = ();
            cid = ("x", "a");
            if (aCity[((0, 2))] == null)
            {
return "region";
            }
            try
            {
                ((6, 4) + "-" + (10, 2) + "-" + (12, 2));
            }
            catch
            {
return "birthday";
            }
            for (int i = 17; i >= 0; i--)
            {
                iSum += ((2, i) % 11) * (cid[17 - i].ToString(), );
            }
            if (iSum % 11 != 1)
            {
return ("Certificate number");
            }

return (aCity[(0, 2))] + "," + (6, 4) + "-" + (10, 2) + "-" + (12, 2) + "," + (((16, 1)) % 2 == 1 ? "Male" : "Female"));

        }