Compilare: main.cpp: In instantiation of 'std::ostream& operator<<(std::ostream&, const std::vector<_Tp>&) [with T = int; std::ostream = std::basic_ostream<char>]': main.cpp:56:11: required from here main.cpp:8:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); ++i) { main.cpp:10:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i != v.size() - 1) os << " "; ~~^~~~~~~~~~~~~~~