Compilare: user.cpp: In function ‘int check(std::string)’: user.cpp:18:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int d = 0; d < k.size(); ++ d) ^ user.cpp: In function ‘int main()’: user.cpp:65:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j + 1 < s.size(); ++ j) ^