Compilare: user.cpp: In function ‘int main()’: user.cpp:50:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<a.size();i++) ~^~~~~~~~~ user.cpp:56:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<b.size();i++) ~^~~~~~~~~ user.cpp:68:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<b.size();i++) ~^~~~~~~~~