Masa - evaluare expresie

#include <bits/stdc++.h>

using namespace std;

ifstream fin("masa.in");
ofstream fout("masa.out");

map<char, int> m;
string s;

int rezolvare(int& i)
{
    stack<int> v;
    v.push(0);

    for( ;i < s.length(); i++)
    {
        if(isalpha(s[i]))
        {
            v.push(m[s[i]]);
        }
        else if(isdigit(s[i]))
        {
            int val = v.top();
            v.pop();
            v.push(val * (s[i] - '0'));
        }
        else if(s[i] == '(')
        {
            i++;
            int rez = rezolvare(i);
            v.push(rez);
        }
        else if(s[i] == ')')
        {
            int mt = 0;
            while(!v.empty())
            {
                mt += v.top();
                v.pop();
            }
            return mt;
        }
    }


    int rezultat = 0;
    while(!v.empty())
    {
        rezultat += v.top();
        v.pop();
    }
    return rezultat;
}

int main()
{
    getline(fin, s);
    m['H'] = 1;
    m['C'] = 12;
    m['O'] = 16;

    int i = 0;
    fout << rezolvare(i);

    return 0;
}