Compilare: user.cpp: In function ‘void df1(int)’: user.cpp:20:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a[k].size(); ++i) ^ user.cpp: In function ‘void df(int, long long int)’: user.cpp:43:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a[k].size(); ++i) ^ user.cpp:59:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < a[k].size(); ++i) ^