Compilare: user.cpp: In function ‘void df(int)’: user.cpp:16:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<a[x].size();i++) ^ user.cpp: In function ‘int main()’: user.cpp:48:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i=0;i<b[x].size();i++) ^