Compilare: user.cpp: In function ‘int main()’: user.cpp:19:28: warning: passing NULL to non-pointer argument 3 of ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::getline(std::basic_istream<_CharT, _Traits>::char_type*, std::streamsize, std::basic_istream<_CharT, _Traits>::char_type) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::char_type = char; std::streamsize = int]’ [-Wconversion-null] f.getline(sir,1000,NULL); ^