Compilare: user.cpp: In function ‘int main()’: user.cpp:19:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (c < s.size() - 2 && s[c] >= s[c+1]) ^ user.cpp:21:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (c == s.size() - 2) ^ user.cpp:21:8: warning: suggest explicit braces to avoid ambiguous ‘else’ [-Wparentheses] if (c == s.size() - 2) ^ user.cpp:34:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; c < s.size() - 1; ++c) ^