bubble sort - listas

#include <iostream>
using namespace std;

struct node {
  int entry = 0; // valores por defecto
  node *next = nullptr;
};

struct lista {
    node* root = nullptr;
};

void mostrar_lista (lista& l) // funciona
{
    for (node *p = l.root; p != 0; p = p->next)
        cout << p->entry << ' ';
    cout << endl << endl;
}

void insertar_nodo_al_final (lista &l, int a) // funciona
{
    node* nuevo = new node;
    nuevo->entry = a;
    if (l.root != 0) // apunta a algo?
    {
        node* p = l.root;
        while (p->next != 0)
            p = p->next;
        p->next = nuevo;
    }
    else
        l.root = nuevo;
}

void swap_entries (node*& a, node*& b)
{
    int aux = a->entry;
    a->entry = b->entry;
    b->entry = aux;
}

void bubble_sort (lista& a)
{
    node* p; node* q; bool swapped = true;

    while (swapped)
    {
        swapped = false;
        p = a.root;
        q = a.root;
        q = q->next;

        while (q != 0)
        {
            if (p->entry > q->entry)
            {
                swap_entries (p,q);
                swapped = true;
            }
            p = p->next;
            q = q->next;
        }
    }
}

int main()
{
    lista L;

    for (int i=10; i>0; i--)
        insertar_nodo_al_final (L, (i+3)%10);

    mostrar_lista(L);

    bubble_sort(L);

    mostrar_lista(L);

    return 0;
}