Equivalent resistance

#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <cmath>

using namespace std;

float round_to_tenth(float a){
    if (int(a*100) % 10 > 5) return (float(int(a*10))/10) + 0.1;
    else return float(int(a*10))/10;
}

int main()
{
    map<string, int> resistors;
    vector<string> names;
    float resistance = 0;
    int n, count = 0;
    cin >> n; cin.ignore();
    for (int i = 0; i < n; i++) {
        string name;
        int r;
        cin >> name >> r; cin.ignore();
        names.push_back(name);
        resistors.insert({name, r});
    }
    string circuit;
    getline(cin, circuit);
    count += std::count(circuit.begin(), circuit.end(), '(');
    count += std::count(circuit.begin(), circuit.end(), '[');
    for (int i = 0; i < circuit.size(); i++) {
        for (auto x: names) {
            if (circuit.find(x) == i) {
                string l = to_string(resistors[x]);
                circuit = circuit.substr(0, i) + l + circuit.substr(i + x.length());
            }
        }
    }
    for (int i = 0; count > 0; i++) {
        string substr;
        float a = 0, b = 0, c = 0;
        if (i > circuit.size()) {
            i = -1;
            continue;
        }
        if (circuit[i] == '(') {
            substr = circuit.substr(i + 1);
            int j = substr.find(')');
            if ((substr.find('[') > j || substr.find('[') == string::npos) && (substr.find('(') > j || substr.find('(') == string::npos)) {
                a = 0, b = 0, c = 0;
                substr = circuit.substr(i, j);
                c = stof(substr.substr(substr.find_last_of(' ')));
                substr = substr.substr(0, substr.find_last_of(' '));
                if (substr.find_last_of(' ') != string::npos) {
                    b = stof(substr.substr(substr.find_last_of(' ')));
                    substr = substr.substr(0, substr.find_last_of(' '));
                }
                if (substr.find_last_of(' ') != string::npos) {
                    a = stof(substr.substr(substr.find_last_of(' ')));
                    substr = substr.substr(0, substr.find_last_of(' '));
                }
                substr = to_string(a + b + c);
                circuit = circuit.substr(0, i) + substr + circuit.substr(j + i + 2);
                count--;
                i = 0;
            }
        }
        if (circuit [i] == '[') {
            substr = circuit.substr(i + 1);
            int j = substr.find(']');
            if ((substr.find('(') > j || substr.find('(') == string::npos) && (substr.find('[') > j || substr.find('[') == string::npos)) {
                a = 0, b = 0, c = 0;
                substr = circuit.substr(i, j);
                c = stof(substr.substr(substr.find_last_of(' ')));
                substr = substr.substr(0, substr.find_last_of(' '));
                if (substr.find_last_of(' ') != string::npos) {
                    b = stof(substr.substr(substr.find_last_of(' ')));
                    substr = substr.substr(0, substr.find_last_of(' '));
                }
                if (substr.find_last_of(' ') != string::npos) {
                    a = stof(substr.substr(substr.find_last_of(' ')));
                    substr = substr.substr(0, substr.find_last_of(' '));
                }
                (b == 0)? substr = to_string(c): (a == 0)? substr = to_string(b * c/ (b + c)) : substr = to_string(a*b*c/(b*c + a*b + a*c));
                circuit = circuit.substr(0, i) + substr + circuit.substr(j + i + 2);
                count--;
                i = 0;
            }
        }
    }
    resistance = round_to_tenth(stof(circuit));
    (resistance == floor(resistance))? cout << resistance << ".0" << endl: cout << resistance << endl;
}