Language: C++

#include<stdio.h>
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
 
 
using namespace std;
 
//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}
 
//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}
 
//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;
 
//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())
 
//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)
 
//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);
 
//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))
 
//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

//pair sort
bool compare_by_b(pair<LL, LL> a, pair<LL, LL> b) {
    if(a.second != b.second){
        return a.second < b.second;
    }else{
        return a.first < b.first;
    }
}


void solve(string S, long long K){
    if(K==1){
        cout<<S[0]<<endl;
    }
    else{
        bool flag=false;
        REP(i,K){
            if(S[i]!='1'){
                cout<<S[i]<<endl;
                return;
            }
        }
        cout<<'1'<<endl;
    }
    return;
}

int main(){
    string S;
    cin>>S;
    long long K;
    scanf("%lld",&K);
    solve(to_string(S), K);
    return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:104:20: error: no matching function for call to 'to_string(std::string&)'
  104 |     solve(to_string(S), K);
      |           ~~~~~~~~~^~~
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from a.cc:8:
/usr/include/c++/14/bits/basic_string.h:4240:3: note: candidate: 'std::string std::__cxx11::to_string(int)'
 4240 |   to_string(int __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4240:17: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'
 4240 |   to_string(int __val)
      |             ~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4259:3: note: candidate: 'std::string std::__cxx11::to_string(unsigned int)'
 4259 |   to_string(unsigned __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4259:22: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'unsigned int'
 4259 |   to_string(unsigned __val)
      |             ~~~~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4275:3: note: candidate: 'std::string std::__cxx11::to_string(long int)'
 4275 |   to_string(long __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4275:18: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'long int'
 4275 |   to_string(long __val)
      |             ~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4294:3: note: candidate: 'std::string std::__cxx11::to_string(long unsigned int)'
 4294 |   to_string(unsigned long __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4294:27: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'long unsigned int'
 4294 |   to_string(unsigned long __val)
      |             ~~~~~~~~~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4310:3: note: candidate: 'std::string std::__cxx11::to_string(long long int)'
 4310 |   to_string(long long __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4310:23: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'long long int'
 4310 |   to_string(long long __val)
      |             ~~~~~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4327:3: note: candidate: 'std::string std::__cxx11::to_string(long long unsigned int)'
 4327 |   to_string(unsigned long long __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4327:32: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'long long unsigned int'
 4327 |   to_string(unsigned long long __val)
      |             ~~~~~~~~~~~~~~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4401:3: note: candidate: 'std::string std::__cxx11::to_string(float)'
 4401 |   to_string(float __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4401:19: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'float'
 4401 |   to_string(float __val)
      |             ~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4411:3: note: candidate: 'std::string std::__cxx11::to_string(double)'
 4411 |   to_string(double __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4411:20: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'double'
 4411 |   to_string(double __val)
      |             ~~~~~~~^~~~~
/usr/include/c++/14/bits/basic_string.h:4421:3: note: candidate: 'std::string std::__cxx11::to_string(long double)'
 4421 |   to_string(long double __val)
      |   ^~~~~~~~~
/usr/include/c++/14/bits/basic_string.h:4421:25: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'long double'
 4421 |   to_string(long double __val)
      |             ~~~~~~~~~~~~^~~~~