Compilare: user.cpp: In function ‘void insert(int, std::string)’: user.cpp:21:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ^ user.cpp: In function ‘int query(int, std::string)’: user.cpp:46:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ^ user.cpp: In function ‘int main()’: user.cpp:71:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int k = 0; k < s.size(); ++k) ^