correct дроби из 10й в 4ю

#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#include <string>
#include <stack>
#include <set>
#include <map>
#define pii pair <int, int>
#define pb(x) push_back(x)
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
void cv(vector <int> &v) {
    for (auto x : v) cout << x << ' ';
    cout << "\n";
}

void cvl(vector <ll> &v) {
    for (auto x : v) cout << x << ' ';
    cout << "\n";
}


void cvv(vector <vector <int> > &v) {
    for (auto x : v) cv(x);
    cout << "\n";
}

void cvb(vector <bool> v) {
    for (bool x : v) cout << x << ' ';
    cout << "\n";
}

void cvs(vector <string>  v) {
    for (auto a : v) {
        cout << a << "\n";
    }
}

void cvp(vector <pii> a) {
    for (auto p : a) {
        cout << p.first << ' ' << p.second << "\n";
    }
    cout << "\n";
}

bool sh = 0;

int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    string s; int n; cin >> s >> n;
    s = s.substr(2, s.size() - 2);
    string str = s;
    int x = stoi(s);
    vector <char> ans;
    for (int i = 0; i < n; ++i) {

        string bef, aft;
        bef = to_string(x);
        x *= 4;
        aft = to_string(x);
        if (sh) {
            cout << "i = " << i << "\n";
            cout << "bef aft = " << bef << ' '<< aft << "\n";
        }
        if (aft.size() > str.size()) {
            if (sh) {
                cout << "add\n";
            }
            ans.push_back(aft[0]);
            aft = aft.substr(1, aft.size() - 1);
        } else {
            if (sh) {
                cout << "zero\n";
            }
            ans.push_back('0');
        }

        x = stoi(aft);
        if (sh) {

            cout << "bef aft x = " << bef << ' '<< aft << ' ' << x << "\n";
        }
        if (x == 0) {
            break;
        }
    }
    cout << "0.";
    for (char i: ans) cout << i;
}