Compilare: user.cpp: In function ‘void make_prefix(std::string, std::vector<int>&)’: user.cpp:16:9: warning: unused variable ‘q’ [-Wunused-variable] int i, q = 0; ^ user.cpp: In function ‘int main()’: user.cpp:44:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < B.length(); ++i) { ^ user.cpp:49:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (q == A.length()) { ^