[C++] Liste duble \ Ordonare telefoane dupa nume

/* ****************************************************************************************
// Sa se creeze o lista dublu inlantuita care are partea de informatie urmatoarele campuri:
 • marca telefon
 • numar telefon
 • pret telefon
// Cerinte:
 • Sa se creeze lista;
 • Sa se ordoneze lista dupa marca telefonului;
 • Sa se afiseze toate telefoanele de pret minim;
**************************************************************************************** */

#include <iostream>
#include <fstream>
#include <string.h>

using namespace std;

struct nod {
    char marca[51];
    long numar;
    int pret;
    nod *urm, *ant;
} *p, *u, *prim;

void create()
{
    p = new nod;
    prim = p;
    cout << "Marca: "; cin >> p -> marca;
    cout << "Numar: "; cin >> p -> numar;
    cout << "Pret: "; cin >> p -> pret;
    p -> ant = NULL;
    cout << '\n';
    while(strcmp(p -> marca, "exit") != 0) {
        u = new nod;
        cout << "Marca: "; cin >> u -> marca;
        cout << "Numar: "; cin >> u -> numar;
        cout << "Pret: "; cin >> u -> pret;
        p -> urm = u;
        u -> ant = p;
        p = u;
    }
    u -> urm = NULL;
}

void afis()
{
    p = prim;
    while ( p -> urm != NULL ) {
        cout << p -> marca << " " << p -> numar << " " << p -> pret << '\n';
        p = p -> urm;
    }
}

void ordonare_marca()
{
    int n, pr;
    bool ok;
    char aux[51];

    do {
        p = prim;
        ok = false;
        while( p -> urm -> urm != NULL ) {
            if ( strcmp(p -> marca, p -> urm -> marca) > 0 ) {
                strcpy(aux, p -> marca);
                strcpy(p -> marca, p -> urm -> marca);
                strcpy(p -> urm -> marca, aux);
                n = p -> numar; p -> numar = p -> urm -> numar; p -> urm -> numar = n;
                pr = p -> pret; p -> pret = p -> urm -> pret; p -> urm -> pret = pr;
                ok = true;
            }
            p = p -> urm;
        }
    } while(ok == true);
}
int main()
{
    create();
    ordonare_marca();
    afis();
    return 0;
}