Compilare: user.cpp: In function ‘std::ofstream& operator<<(std::ofstream&, const Huge&)’: user.cpp:46:25: warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: fout << num.v[num.v[0]]; ^ In file included from /usr/include/c++/5/ostream:638:0, from /usr/include/c++/5/istream:39, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /usr/include/c++/5/ccomplex:38, from /usr/include/x86_64-linux-gnu/c++/5/32/bits/stdc++.h:52, from user.cpp:1: /usr/include/c++/5/bits/ostream.tcc:105:5: note: candidate 1: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char; _Traits = std::char_traits<char>] basic_ostream<_CharT, _Traits>:: ^ user.cpp:45:11: note: candidate 2: std::ofstream& operator<<(std::ofstream&, const Huge&) ofstream& operator << (ofstream& fout, const Huge& num) { ^ user.cpp: In function ‘void solve_test()’: user.cpp:68:18: warning: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: fout << ans << '\n'; ^ In file included from /usr/include/c++/5/istream:39:0, from /usr/include/c++/5/sstream:38, from /usr/include/c++/5/complex:45, from /usr/include/c++/5/ccomplex:38, from /usr/include/x86_64-linux-gnu/c++/5/32/bits/stdc++.h:52, from user.cpp:1: /usr/include/c++/5/ostream:508:5: note: candidate 1: std::basic_ostream<char, _Traits>& std::operator<<(std::basic_ostream<char, _Traits>&, char) [with _Traits = std::char_traits<char>] operator<<(basic_ostream<char, _Traits>& __out, char __c) ^ user.cpp:45:11: note: candidate 2: std::ofstream& operator<<(std::ofstream&, const Huge&) ofstream& operator << (ofstream& fout, const Huge& num) { ^