Compilare: user.cpp: In function ‘std::vector<int> unite(const std::vector<int>&, const std::vector<int>&)’: user.cpp:11:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp:11:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp:19:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size()) ^ user.cpp:21:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (j < b.size()) ^ user.cpp: In function ‘std::vector<int> intersect(const std::vector<int>&, const std::vector<int>&)’: user.cpp:31:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp:31:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp: In function ‘std::vector<int> diff(const std::vector<int>&, const std::vector<int>&)’: user.cpp:46:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp:46:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size() && j < b.size()) ^ user.cpp:54:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < a.size()) ^ user.cpp: In function ‘std::ostream& operator<<(std::ostream&, const std::vector<int>&)’: user.cpp:70:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < v.size(); ++ i) ^