Add to linked list

gistfile1.txt

private Node Add(Node a, Node b)
        {
            Node c = null, answer = null;
            int carry = 0;
            while (a != null && b != null)
            {
                carry += a.digit + b.digit;
                if (c == null)
                    answer = c = new Node(carry % 10, null);
                else
                    c = c.next = new Node(carry % 10, null);
                carry /= 10;
                a = a.next;
                b = b.next;

            }
            Node i = (a != null) ? a : b; // bigger number is still left
            while (i != null)
            {
                carry += i.digit;
                if (c == null)
                    answer = c = new Node(carry % 10, null);
                else
                    c = c.next = new Node(carry % 10, null);
                carry /= 10;
                i = i.next;
            }
            while (carry > 0) //left over carry
            {
                c = c.next = new Node(carry % 10, null);
                carry /= 10;
            }
            return answer;
        }