Alien Invasion II

input/code.cpp: In function 'int sum_of_digits(std::__cxx11::string)':
input/code.cpp:8:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0; i<n.length(); ++i) {
                ~^~~~~~~~~~~

#include <bits/stdc++.h>
using namespace std;

#include <sstream>

int sum_of_digits (string n) {
  int sum = 0;
  for(int i=0; i<n.length(); ++i) {
    int aux = n[i]-'0';
    sum += aux;
  }
  return sum;
}

int main() {
  string n;
  cin >> n;

  int sum = sum_of_digits(n);
  int aux = 3;
  while (aux < sum) aux += 3;
  int add = aux - sum;

  ostringstream oss;
  oss << add << n;

  istringstream iss(oss.str());
  int num;
  iss >> num;

  cout << num << endl << 3 << ' ' << num/3 << endl;
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER