Compilare: user.cpp: In function ‘TrieNode* insert(TrieNode*, std::string, int)’: user.cpp:30:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (l == w.length()) ^ user.cpp: In function ‘TrieNode* remove(TrieNode*, std::string, int)’: user.cpp:56:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (l < w.length()) ^ user.cpp:66:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (l == w.length()) ^ user.cpp: In function ‘int get_number_of_occurences(std::string)’: user.cpp:92:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (l == w.length()) return node->words; ^ user.cpp: In function ‘int get_longest_prefix_length(std::string)’: user.cpp:108:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (l == w.length()) return l; ^