#include<iostream>
#include<string>
using namespace std;

int main(void)
{

    char a, b;
    a='1';
    b='2';
    cout<<stoi(a)+stoi(b);
    return 0;
}

In function 'int main()':
Line 11: error: 'stoi' was not declared in this scope
compilation terminated due to -Wfatal-errors.