pilas con listas

#include <iostream>

using namespace std;

struct nodo {
    int entry = 0;
    nodo* next = nullptr;
};

struct stack {
    nodo* top = nullptr;
};

bool is_stack_empty (stack& s)
{
    return s.top == nullptr;
}

stack& push (stack& s, int v)
{
    nodo* nuevo = new nodo;
    nuevo->entry = v;
    nuevo->next = s.top;
    s.top = nuevo;
    return s;
}

stack& pop (stack& s, int& v)
{
    nodo* old_top = s.top;
    s.top = s.top->next;
    v = old_top->entry;
    delete old_top;
    return s;
}

void vaciar_stack (stack& s)
{
    int d;
    while (not is_stack_empty(s))
    {
        pop(s,d);
        cout << d << ' ';
    }
    cout << endl;
}