栈：

using System;

namespace DataStructure.Stack
{
    /// <summary>
    /// Class1 的摘要说明。
    /// </summary>
    class StackNode
    {
        Object item;
        StackNode link;
    }
    class Stack
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            //
            // TODO: 在此处添加代码以启动应用程序
            //
        }

        class Stack
        {
            private StackNode topNode;

            public boolean empty()
            {
                return (topNode==null);
            }

            public void push(Object X)
            {
                StackNode newNode=new StackNode();
                newNode.item=X;
                newNode.link=topNode;
                topNode=newNode;
            }

            public Object pop()
            {
                if(topNode==null)
                {
                    return null;
                }
                else
                {
                    StackNode tempNode=topNode;
                    topNode=topNode.link;
                    return tempNode.item;
                }
            }
            public Object peek()
            {
                if(topNode==null)
                {
                    return null;
                }
                else
                {
                    return topNode.item;
                }
            }
        }
    }
}