Compilare: user.cpp: In function ‘void back(int)’: user.cpp:19:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v[k].size(); i++) ^ user.cpp:22:55: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0 ; j < fp[v[k][i]].size(); j++) ^ user.cpp:26:54: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < fp[v[k][i]].size(); j++) ^