Compilare: user.cpp: In function ‘std::vector<int> sum(std::vector<int>, std::vector<int>)’: user.cpp:13:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = 0; i < b.size(); ++i) { ^ user.cpp:18:51: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = b.size(); i < a.size(); ++i) { ^ user.cpp:25:44: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = 0; i < a.size(); ++i) { ^ user.cpp:30:51: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = a.size(); i < b.size(); ++i) { ^ user.cpp: In function ‘std::vector<int> prod(std::vector<int>, int)’: user.cpp:44:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(register int i = 0; i < a.size(); ++i) { ^