Swap neighbor character in string in c#:

            string str = "TAPAN";
            Console.WriteLine("Before Swaping :"+str);
            string str1 = "";
            Console.Write("After Swaping :");
            for (int i = 0; i < str.Length; i = i + 2)
            {
                int j = 0;
                if (str.Length % 2 != 0 && i == str.Length - 1) { j = 1; }
                str1 += j == 0 ? str[i + 1].ToString() : "";
                str1 += str[i].ToString();
            }
            Console.WriteLine(str1);