Compilare: user.cpp: In function ‘int main()’: user.cpp:20:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i+1 < s.size() && s[i] >= s[i+1]) i++; ^ user.cpp:22:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; i < s.size() - 1;) ^ user.cpp:26:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i+1 < s.size() && s[i] <= s[i+1]) i++; ^ user.cpp:31:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i+1 < s.size() && s[i] >= s[i+1]) i++; ^