UVA-1586 Molar mass

#include <iostream>
#include <stdlib.h>
#include <string>
#include <vector>
#include <algorithm>
#include <string.h>
#include <stack>
#include <unordered_map>
#include <math.h>
#include <iomanip>

using namespace std;

vector<double> molar2MassList {12.01,1.008,16.00,14.01};
enum molarList {C,H,O,N};

int main()
{
    int T;
    cin >> T;
    while(T --)
    {
        string input;
        cin >> input;
        double result = 0;
        for(int i = 0; i < input.size(); i ++)
        {
            enum molarList state;
            double num = 0;
            int digit = 0;
            if(input[i]=='C')
            {
                state = C;
                result += molar2MassList[state];
            }
            else if(input[i]=='H')
            {
                state = H;
                result += molar2MassList[state];
            }
            else if(input[i]=='O')
            {
                state = O;
                result += molar2MassList[state];
            }
            else if(input[i]=='N')
            {
                state = N;
                result += molar2MassList[state];
            }
            else
            {
                while(isdigit(input[i]))
                {
                    num = pow(10,digit++) * num + (input[i++]-'0');
                }
                result += (num-1)*molar2MassList[state];
                i --;
            }
        }
        cout << fixed << setprecision(3) << result << endl;
    }
    return 0;
}