/in/foo.cc: In function 'int main()':
/in/foo.cc:39:30: error: invalid use of member function 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::length() const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type = long unsigned int]' (did you forget the '()' ?)
     for (size_t i = 0; i < s.length; i++)
                            ~~^~~~~~