2 排数字穿插起来

      string a = "1,2,3,4";
            string b = "5,6,7,8";
            string[] arra = a.Split(',');
            string[] arrb = b.Split(',');
            string c = "";
            for (int i = 0; i < arra.Length; i++)
            {
                c += arra[i] + "-" + arrb[i] + ",";
            }
            Console.WriteLine(c.TrimEnd(','));