Compilare: user.cpp: In member function 'void trie::add(std::string)': user.cpp:24: warning: comparison between signed and unsigned integer expressions user.cpp: In member function 'int trie::search(std::string)': user.cpp:33: warning: comparison between signed and unsigned integer expressions user.cpp: In member function 'int trie::prefix(std::string)': user.cpp:41: warning: comparison between signed and unsigned integer expressions user.cpp: In member function 'void trie::erase(std::string)': user.cpp:49: warning: comparison between signed and unsigned integer expressions