Compilare: user.cpp: In function ‘void pushToTrie(Trie*, int)’: user.cpp:44:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size()) { ^ user.cpp: In function ‘bool popFromTrie(Trie*, int)’: user.cpp:57:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (letter == str.size()) { // finished the current word ^ user.cpp: In function ‘int getNumberOfWords(Trie*, int)’: user.cpp:79:28: 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 getNumberOfPrefixes(Trie*, int)’: 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 there isn't a child with words' next character ^