Compilare: user.cpp: In function ‘int main()’: user.cpp:15:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=2; i<a.size(); i++){ ^ user.cpp:21:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=1; i<b.size(); i++){ ^ user.cpp:24:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(j==a.size()-1){ ^