Compilare: user.cpp: In function ‘void insert_word(std::string)’: user.cpp:18:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<str.size();++i) ^ user.cpp: In function ‘void delete_word(std::string)’: user.cpp:30:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<str.size();++i) ^ user.cpp: In function ‘int words_query(std::string)’: user.cpp:41:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<str.size();++i) ^ user.cpp: In function ‘int pre_query(std::string)’: user.cpp:52:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0;i<str.size();++i) ^