#include <iostream>
using namespace std;
class Stack
{
private:
  struct Node
  {
    int data;
    Node *next;
  };
  Node *head;
  Node *p;
  int length;

public:
  Stack()
  {
    head = NULL;
    length = 0;
  }
  void push(int n)//入栈
  {
    Node *q = new Node;
    q->data = n;
    if (head == NULL)
    {
      q->next = head;
      head = q;
      p = q;
    }
    else
    {
      q->next = p;
      p = q;
    }
    length ++;
  }

  int pop()//出栈并且将出栈的元素返回
  {
    if (length <= 0)
    {
      abort();
    }
    Node *q;
    int data;
    q = p;
    data = p->data;
    p = p->next;
    delete(q);
    length --;
    return data;
  }
  int size()//返回元素个数
  {
    return length;
  }
  int top()//返回栈顶元素
  {
    return p->data;
  }
  bool isEmpty()//判断栈是不是空的
  {
    if (length == 0)
    {
      return true;
    }
    else
    {
      return false;
    }
  }
  void clear()//清空栈中的所有元素
  {
    if (length > 0)
    {
      pop();
    }
  }
};
int main()
{
  //以下为测试代码
  Stack s;
  s.push(1);
  s.push(2);
  s.push(3);
  while(!s.isEmpty())
  {
    cout<<s.pop()<<endl;
  }
  return 0;
}

#include <iostream>
using namespace std;
template<class T>class Stack
{
private:
  struct Node
  {
    T data;
    Node *next;
  };
  Node *head;
  Node *p;
  int length;

public:
  Stack()
  {
    head = NULL;
    length = 0;
  }
  void push(T n)//入栈
  {
    Node *q = new Node;
    q->data = n;
    if (head == NULL)
    {
      q->next = head;
      head = q;
      p = q;
    }
    else
    {
      q->next = p;
      p = q;
    }
    length ++;
  }

  T pop()//出栈并且将出栈的元素返回
  {
    if (length <= 0)
    {
      abort();
    }
    Node *q;
    int data;
    q = p;
    data = p->data;
    p = p->next;
    delete(q);
    length --;
    return data;
  }
  int size()//返回元素个数
  {
    return length;
  }
  T top()//返回栈顶元素
  {
    return p->data;
  }
  bool isEmpty()//判断栈是不是空的
  {
    if (length == 0)
    {
      return true;
    }
    else
    {
      return false;
    }
  }
  void clear()//清空栈中的所有元素
  {
    while(length > 0)
    {
      pop();
    }
  }
};
int main()
{
  Stack<char> s;
  s.push('a');
  s.push('b');
  s.push('c');
  while(!s.isEmpty())
  {
    cout<<s.pop()<<endl;
  }
  return 0;
}