Compilare: user.cpp: In function ‘int main()’: user.cpp:14:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) ^ user.cpp:16:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (s[i] <= s[i+1] && i < s.size()) ^ user.cpp:20:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (s[i] >= s[i+1] && i < s.size()) ^