Compilare: user.cpp: In function ‘int main()’: user.cpp:47:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] (vec[i].size() == r ? grad_r : grad_r_minus).push_back(i); } ^ user.cpp:51:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < grad_r.size(); ++i){ ^ user.cpp:54:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < grad_r_minus.size(); ++i){ ^ user.cpp:72:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < grad_r.size(); ++i){ ^ user.cpp:75:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(dr[i] < grad_r.size()){ ^