Compilare: user.cpp: In function ‘bool exist(int)’: user.cpp:10:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i=0;i<a[m].size();i++){ ^ user.cpp: In function ‘void del(int)’: user.cpp:29:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<a[m].size();i++){ ^