Alien Invasion II

input/code.cpp: In function 'int main()':
input/code.cpp:18:22: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int add = 3 - (s % 3);
                   ~~~^~~~

#include <iostream>
#include <string>

using namespace std;

int main() {
    int x;
    cin >> x;
    int t = x;
    int s, m;
    while(x > 0)    
    {    
        m = x % 10;    
        s += m;    
        x /= 10;    
    }  
    cout << s << endl;
    int add = 3 - (s % 3);
    string str = to_string(add) + to_string(t);
    cout << str << endl;
    x = stoi(str);
    cout << 3 << " " << x / 3;
    return 0;
}

Test 1

Verdict: RUNTIME ERROR

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

Test 2

Verdict: RUNTIME ERROR

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

Test 3

Verdict: RUNTIME ERROR

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