Compilare: user.cpp: In function ‘int main()’: user.cpp:20:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<A.size(); i++) ^ user.cpp:31:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<A.size(); i++) ^ user.cpp:42:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=A.size(); i<B.size(); i++) ^