cong and nhan

#include <sstream>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <cctype>
#include <string>
using namespace std;

int check_to_number(string s)
{
    int check = 1, l = s.length();
    for (int i = 0; i<l; i++)
        if (!isdigit(s[i]) && s[i] != '.')
        {
            check = 0;
            break;
        }
    return check;
}

float convert_to_number(string s)
{
    float number;
    stringstream ss (s);
    ss >> number;
    return number;
}

float process(string s, int l, int r)
{
    int li = 0, ri = r;
    if (check_to_number(s)) return convert_to_number(s);
    else
    {
        int i;
        for (i=li; i<ri; i++) if (s[i] == '+') return process(s.substr(li, i-li), li, i) + process(s.substr(i+1, ri-i), i+1, ri);
        for (i=li; i<ri; i++) if (s[i] == '*') return process(s.substr(li, i-li), li, i) * process(s.substr(i+1, ri-i), i+1, ri);
    }
}

int main()
{
    float number;
    string s = "5+8*6+3";
    number = process(s,0,s.length());
    cout<<number;
    return 0;
}