ИТМО. N1

#include <iostream>
#include <vector>
#include <cmath>
#include <vector>
#include <string>
#include <cstdio>
#include <algorithm>
using namespace std;
using ll = long long;

bool less_10(char some){
    if (some=='0'||some=='1'||some=='2'||some=='3'||some=='4'||some=='5'||some=='6'||some=='7'||some=='8'||some=='9'){
        return true;
    } else{
        return false;
    }
}

int to_num(char a){
    int res;
    if (less_10(a)){
        res = a - 48;
    }else{
        res =  a - 'A' + 10;
    }
    return res;
    //cout<< res<<'\n';
}

char to_char(ll x){
    char res;
    if (x < 10){
        res = x + 48;
    }else{
        res = x - 10 + 'A';
    }
    return res;
    //cout<<res<<'\n';
}


string to_str(int x){
    string res = to_string(x);
    return res;
}



ll helper(string num, int from){
    //1 -- перевести в десятичную
    string ans = ""; // в конце перевернём эту строку
    int sz = num.length();
    ll real = 0;
    for(int i = 1; i <= sz; ++i){
        char some = num[i-1]; //digit
        int dig;
        if (less_10(some)){
            dig = some - '0';
        }
        else{
            dig = to_num(some);
        }
        real += dig * pow(from, sz-i);
    }
    return real;
}
//2 -- перевести из десятичной в нужную систему
string convert(ll tenth, int to){
    ll num = tenth;
    string S_num = to_string(num);
    string ans = "";
    while (num > 0){
        char sym; //symbol
        ll dig =  num % to;
        sym = to_char(dig);
        ans += sym;
        num /= to;
    }
    //reverse(ans.begin(), ans.end());
    //return ans;
    ans = ans.substr(0, 2);
    reverse(ans.begin(), ans.end());
    return ans;
}

string convertX(ll tenth, int to){
    ll num = tenth;
    string S_num = to_string(num);
    string ans = "";
    while (num > 0){
        char sym; //symbol
        int dig =  num % to;
        sym = to_char(dig);
        cout<<"dig = "<<dig<<'\n';
        ans += sym;
        num /= to;
    }
    reverse(ans.begin(), ans.end());
    return ans;
}

int main()
{
    /*string num;
    int to, from;
    cin>>from>>num>>to;
    int tenth = helper(num,from);
    string result = convert(tenth, to);
    cout<<result<<'\n';*/
    //1 трактовка: (21 in 16th sys) ^ N
    ll sx21 = helper("21", 16);
    cout<<sx21<<'\n';
    for (ll x = 1; x <= 10;++x){
        cout<<"x = "<<x<<'\n';
        for (ll n = 1;n<=x;++n){
            ll d = pow(sx21, n);
            string s = convert(d, 16);
            //reverse(s.begin(), s.end());
            cout<<"nds= "<<n<<' '<<d<<' '<<s<<'\n';
            //string y = s[1] + s[0];
            ll pl = helper(s, 16);
        }cout<<'\n';
    }
    cout<<"check\n";
    ll q = 1406408618241;
    string r = convertX(q, 16);
    cout<<"r= "<<r<<'\n';
}