/in/foo.cc: In member function 'bool Solution::isHappy(int)':
/in/foo.cc:4:9: error: 'string' was not declared in this scope
         string  str;
         ^~~~~~
/in/foo.cc:8:13: error: 'str' was not declared in this scope
             str = to_string(tmp);
             ^~~
/in/foo.cc:8:32: error: 'to_string' was not declared in this scope
             str = to_string(tmp);
                                ^
/in/foo.cc:10:26: error: unable to deduce 'auto&&' from 'str'
             for(auto c : str)
                          ^~~