Compilare: user.cpp: In function ‘long long unsigned int max_dif(const std::vector<int>&)’: user.cpp:13:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0, j = 1; j < cifre.size(); i++, j++) ~~^~~~~~~~~~~~~~ user.cpp:16:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int k = 0; k < cifre.size(); k++) ~~^~~~~~~~~~~~~~ user.cpp: In function ‘int main()’: user.cpp:32:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 1; i <= n; i++) ~~^~~~