void Pop()
        {
            if (top == null)
            {
                throw new Exception("No Element to POP");
            }
            SNode tempNode = top;

            top      = tempNode.NextSNode;
            tempNode = null;
        }
        void Push(int x)
        {
            SNode newNode = new SNode(x);

            if (top == null)
            {
                top = newNode;
                return;
            }
            newNode.NextSNode = top;
            top = newNode;
            return;
        }