Kyselyt

#include <iostream>
#include <sstream>
#include <cmath>

using namespace std;
typedef long long ll;

ll
decade(ll n)
{
	ll sum; 

	sum = 0;
	for (int i = 1; i < 1000000; i++) {
		if (sum + i*9*pow(10.0, i-1) > n)
			return i;
		else
			sum += i*9*pow(10.0, i-1);
	}
	return 0;
}

ll
sums(ll decade)
{
	ll sum;

	sum = 0;
	for (int i = 1; i < decade; i++) 
		sum += i*9*pow(10.0, i-1);
	return sum;
}

int
main(int argc, char **argv)
{
	int q;
	cin >> q;
	ll qs[q];
	for (int i = 0; i < q; i++) {
		cin >> qs[i];
	}
	for (int i = 0; i < q; i++) {
		ll inth, nth, dec, s, sm;
		
		dec = decade(qs[i]);
		s = sums(dec);
		sm = qs[i] - s;
		nth = (ll)ceil((double)sm/(double)dec);
		inth = nth % dec;
		stringstream ss;
		ss << nth;
		string str = ss.str();
		cout << str.at(inth) << endl;
	}
	return 0;
}

Test 1

Group: 1

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::at

Test 2

Group: 2

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::at

Test 3

Group: 3

Verdict: RUNTIME ERROR

terminate called after throwing an instance of 'std::out_of_range'
  what():  basic_string::at