Compilare: user.cpp: In function ‘int main()’: user.cpp:23:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<v1.size();i++){ ^ user.cpp:26:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<v2.size();i++){ ^ user.cpp:29:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<v3.size();i++){ ^