C#实现栈

using System;
using System.Collections.Generic;
using System.Text;
namespace Stack
{
    public class Stack
    {
        private Node first = null;
        private int count = 0;
        public bool Empty
        {
            get
            {
                return (first == null);
            }
        }
        public int Count
        {
            get
            {
                return count;
            }
        }
        //Push
        public void Push(object o)
        {
            first = new Node(o,first);
            count++;
        }
        //Pop
        public object Pop()
        {
            if (first == null)
            {
                throw new InvalidOperationException("Can't Pop from an empty stack.");
            }
            else
            {
                object temp = first.Value;
                first = first.Next;
                count--;
                return temp;
            }
        }
    }
    class Node
    {
        public Node Next;
        public object Value;
        public Node(object value) : this(value, null) { }
        public Node(object value, Node next)
        {
            Next = next;
            Value = value;
        }
    }
    class StackApp
    {
        static void Main(string[] args)
        {
            Stack s = new Stack();
            if (s.Empty) Console.WriteLine("堆栈为空。");
            else Console.WriteLine("堆栈非空。");
            for (int i = 0; i < 5; i++)
            {
                s.Push(i);
            }
            Console.WriteLine("往堆栈中压入了{0}个元素。",s.Count);
            for (int i = 0; i < 5; i++)
            {
                Console.WriteLine("弹出第{0}个元素，还剩{1}个元素。",(int)s.Pop()+1,s.Count);
            }
            s = null;
            Console.ReadKey();
        }
    }
}