Compilare: user.cpp: In function ‘void insert(std::string)’: user.cpp:34:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<w.length();++i) ^ user.cpp: In function ‘void erase(std::string)’: user.cpp:51:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<w.length(); ++i) ^ user.cpp: In function ‘int prefix(std::string)’: user.cpp:66:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<w.length(); ++i) ^ user.cpp: In function ‘int nrapp(std::string)’: user.cpp:81:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0; i<w.length(); ++i) ^