#include <iostream>
#include <malloc.h>
using namespace std;

typedef struct linknode
{
    int data;
    struct linknode *next;
}Listack;

//初始化棧
void init(Listack *&s)
{
    s=(Listack*)malloc(sizeof(Listack));
    s->next=NULL;
}
//摧毀棧
void destroy(Listack *&s)
{
    Listack *p=s,*q=s->next;
    while(q!=NULL)
    {
        free(p);
        p=q;
        q=q->next;
    }
    free(p);
}
//判斷棧是否為空
bool empty(Listack *s)
{
    return s->next==NULL;
}
//進棧
void push(Listack *&s,int e)
{
    Listack *q;
    q=(Listack*)malloc(sizeof(Listack));
    q->next=s->next;
    q->data=e;
    s->next=q;
}
//出棧
void pop(Listack *&s)
{
    if(s->next==NULL)
    {
        cout<<"棧為空，不能刪除!";
        return;
    }
    Listack *p;
    p=s->next;
    s->next=p->next;
    free(p);
}
//取棧頂元素
int top(Listack *&s)
{
    if(s->next==NULL)
    {
        cout<<"棧為空，無元素！";
        return 0;
    }
    Listack *p;
    p=s->next;
    return p->data;
}


int main()
{
    Listack *s;
    init(s);
    push(s,2);
    push(s,4);
    cout<<top(s)<<endl;
    pop(s);
    cout<<top(s)<<endl;
    return 0;
}