Compilare: user.cpp: In function ‘bool check_freqs(std::string, int, std::string*)’: user.cpp:23:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ^ user.cpp:32:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < seen.size(); ++i) { ^ In file included from user.cpp:3:0: user.cpp: In function ‘int main()’: user.cpp:62:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] assert(s.size() == n); ^