用C#编写1个类实现堆栈的功能

以下是一个栈：

class Entry
{
public int Data;
public Entry Next;
}

class Stack
{
Entry entry;

public Stack()
{
entry=new Entry();
entry.Next=null;
}

public void Push(int data)
{
Entry e=new Entry();
e.Data=data;
e.Next=entry;
entry=e;
}

public Entry Pop()
{
if(entry.Next==null)
{
return null;
}

Entry e=new Entry();
e.Data=entry.Data;
e.Next=entry.Next;
entry=entry.Next;
return e;
}

}