Compilare: user.cpp: In function ‘bool exista(int, int)’: user.cpp:12:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0;j < v[i].size();++j) ^ user.cpp: In function ‘int main()’: user.cpp:42:37: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j=0;j<v[i].size();++j) ^