Solucion Gaston

#ifndef BIGNUMBER_H_INCLUDED
#define BIGNUMBER_H_INCLUDED

#include <iostream>
#include <algorithm>

using namespace std;

class BigNumber
{
private:
    string n;
public:
    BigNumber(string _n); ///Constructor
    string toStr(); ///Devolver string
    BigNumber operator*(BigNumber &b); ///Operador multiplicar
};

BigNumber::BigNumber(string _n)
{
    this->n = _n;
}

string BigNumber::toStr()
{
    return this->n;
}

string multiplicar(string a, string b)
{
    int tam = a.size()+b.size()+10; ///+10 changui
    int res[tam], p;

    for(int i=0; i<tam; i++)
        res[i] = 0;

    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());

    for(int i=0; i<a.size(); i++)
    {
        for(int j=0; j<b.size(); j++)
        {
            p = (a[i]-'0')*(b[j]-'0');
            res[i+j] += p%10;
            res[i+j+1] += p/10;
        }
    }

    for(int i=0; i<tam-1; i++)
    {
        if(res[i] > 9)
        {
            res[i+1] += res[i]/10;
            res[i] %= 10;
        }
    }

    int maxPos = tam-1;
    while(maxPos >= 0 && res[maxPos] == 0)
        maxPos--;

    string r(maxPos+1, ' ');
    for(int i=maxPos; i>=0; i--)
        r[maxPos-i] = (res[i]+'0');

    return r;
}

BigNumber BigNumber::operator*(BigNumber &num)
{
    return multiplicar(this->toStr(), num.toStr());
}

ostream &operator<<(ostream &out, BigNumber &num)
{
    return out << num.toStr();
}

#endif // BIGNUMBER_H_INCLUDED