Compilare: user.cpp: In function ‘void pushToTrie(TrieNode*, int, std::string&)’: user.cpp:43:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size()) { // finished the current word ^ user.cpp: In function ‘bool popFromTrie(TrieNode*, int, std::string&)’: user.cpp:56:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size()) { // finished the current word ^ user.cpp: In function ‘int getNumberOfWords(TrieNode*, int, std::string&)’: user.cpp:78:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size()) // we have reached the end of the word ^ user.cpp: In function ‘int getLengthOfPrefix(TrieNode*, int, std::string&)’: user.cpp:90:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size() || node->child[str[letter] - 'a'] == NULL) // if I've finished the current word or ^