Compilare: user.cpp: In function ‘void prefix(std::string)’: user.cpp:23:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < s.size()) ^ user.cpp: In function ‘int main()’: user.cpp:58:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (j < s.size()) ^ user.cpp:65:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (q == s2.size()) ^ user.cpp:91:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = last + 1; i < s.size(); i++) ^