解决两个小问题,送积分

Question

// Stack名字空间
namespace Stack
{
    using System;    public class Stack
    {
        
        private Node first = null;       
        private int count = 0;     
        public bool Empty
        {
            get
            {
                return (first == null);
            }
        }       
        public int Count
        {
            get
            {
                return count;
            }
        }        
        public object Pop()
        {
            if (first == null)
            {
                throw new InvalidOperationException("Cant pop from an empty stack");
            }
            else
            {
                object temp = first.Value;                
                first = first.Next;//这里的Next为什么会自动到下一个，
                count--;
                return temp;
            }
        }       
        public void Push(object o)
        {
            first = new Node(o, first);//这里只是个构造函数，对联Next,Value进行了初始化
            count++; 
        }        
        class Node
        {
            
            public Node Next;
            public object Value;//这时原类型为什么要声明为object 类型，Node类型或其它类型不行吗？            public Node(object value) : this(value, null) { }            public Node(object value, Node next)
            {
                Next = next;
                Value = value;
            }
        }
    }    class StackApp
    {
        static void Main()
        {
            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("弹出了第{0}个元素，还剩{1}个元素。", (int)s.Pop() + 1, s.Count);            s = null;
        }
    }
}