Compilare: user.cpp: In function ‘int main()’: user.cpp:14:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (c < s.size() - 1) ^ user.cpp:16:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (s[c] <= s[c+1] && c < s.size() - 1) ^ user.cpp:20:49: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (s[c] >= s[c+1] && c < s.size() - 1) ^