#include<iostream>
using namespace std;

struct node
{
    node * next;
    int val;
};

bool isEmpty(node *stack)
{
    if (stack)
    {
        return false;
    }
    else return true;
}
void showTop(node *stack)
{
    if (isEmpty(stack))
    {
        cout << "stack is empty!" << endl;
    }
    else cout << stack->val<<endl;
}

void push(node *&stack, int v)
{
    node * e = new node;
    e->val = v;
    e->next = stack;
    stack = e;
}
void pop(node *&stack)
{
    if (!isEmpty(stack))
    {
        node * e = stack;
        stack = stack->next;
        delete e;
    }
}


int main()
{
    node * head = nullptr;
    node * tail = nullptr;
    node * stack = nullptr;
    pop(stack);
    showTop(stack);
    pop(stack);
    showTop(stack);
    push(stack, 5);
    showTop(stack);
    push(stack, 1);
    showTop(stack);
    push(stack, 3);
    showTop(stack);
    pop(stack);
    showTop(stack);



    system("pause");
    return 0;
}