Compilare: user.cpp: In function ‘int main()’: user.cpp:53:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<v1.size();i++) ^ user.cpp:60:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<v2.size();i++) ^ user.cpp:67:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<v3.size();i++) ^