[C++]Arbori binari cu pointeri

#include <iostream>

using namespace std;

struct nod
{
    int cheie;
    nod *st, *dr;
};
nod *rad, *p;
int val;

void adauga(nod *&c, int val)
{
    if(c != 0)
        if(c->cheie == val)
            cout<<"Acest nod exista deja!";
        else if(c->cheie < val)
            adauga(c->dr, val);
        else
            adauga(c->st, val);
    else
    {
        c = new nod;
        c->cheie = val;
        c->st = 0;
        c->dr = 0;
    }
}

void preord (nod *p)
{
    cout<<p->cheie<<" ";
    if(p->st != 0) preord(p->st);
    if(p->dr != 0) preord(p->dr);
}

void inord (nod *p)
{
    if(p->st != 0) inord(p->st);
    cout<<p->cheie<<" ";
    if(p->dr != 0) inord(p->dr);
}

void postord (nod *p)
{
    if(p->st != 0) postord(p->st);
    if(p->dr != 0) postord(p->dr);
    cout<<p->cheie<<" ";
}

void cauta (nod *p, int x)
{
    if(p==NULL)
        cout<<"Nu exista informatia in arbore.\n";
    else if(x < p->cheie)
        cauta(p->st, x);
    else if(x > p->cheie)
        cauta(p->dr, x);
    else
        cout<<"Nodul cautata a fost gasit.\n";
}

int main()
{
    rad=NULL;
    do
    {
        cout<<"Dati valoarea: "; cin>>val;
        if(val != 0) adauga(rad, val);
    }
    while(val != 0);
    cout<<"\n Parcurgearea in preordine: "<<endl;
    preord(rad);
    cout<<"\n Parcurgerea in inordine: "<<endl;
    inord(rad);
    cout<<endl;
    cout<<"\n Parcurgerea in postordine: "<<endl;
    postord(rad);
    cout<<endl;
    cout<<"\n Informatia de cautat: "; cin>>val;
    cauta(rad, val);
    cout<<endl;
    return 0;
}