Compilare: user.cpp: In function ‘void add(std::string)’: user.cpp:27:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < s.size(); ++i) { ^ user.cpp: In function ‘void count(std::string)’: user.cpp:67:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < s.size(); ++i) { ^ user.cpp: In function ‘void search(std::string)’: user.cpp:83:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i = 0; i < s.size(); ++i) { ^