c++中栈的基本实现stack

#include
using namespace std;

typedef char Elm;

struct node
{
Elm data;
node* next;
};

node* top=NULL;//顶指针
node* low=NULL;//低指针

void push(Elm A)
{
node *r=new node;r->data=A;r->next=NULL;
if(top==NULL)
{
low=r;
top=r;
}
else
{
node* s=top;
r->next=s;
top=r;
}
}

void pop()//弹出栈顶元素
{
if(top==NULL)
{
low=NULL;
cout<<"栈无元素，弹出失败！";
return ;
}
node *s=top;
top=s->next;
delete s;
}

Elm front()//获得栈顶元素
{
if(top==NULL)
{
cout<<"栈无元素，获取失败！";
return '0';
}
else
{
return top->data;
}
}