Compilare: main.cpp: In member function 'void Trie::add(std::__cxx11::string)': main.cpp:34:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(++i!=s.size() && x->next[s[i]-'a']!=NULL)///search until end of word or node not allocated ~~~^~~~~~~~~~ main.cpp:37:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i!=s.size())///word is not already in trie => new descendant ~^~~~~~~~~~ main.cpp:41:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(++i!=s.size())///allocate new nodes until end of word ~~~^~~~~~~~~~ main.cpp: In member function 'void Trie::cut(std::__cxx11::string)': main.cpp:57:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(++i!=s.size() && x->next[s[i]-'a']!=NULL)///search until end of word ~~~^~~~~~~~~~ main.cpp: In member function 'int Trie::operator[](std::__cxx11::string)': main.cpp:80:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(++i!=s.size() && x->next[s[i]-'a']!=NULL)///search until end of word or node not allocated ~~~^~~~~~~~~~ main.cpp:83:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if(i!=s.size())///word not in trie ~^~~~~~~~~~ main.cpp: In member function 'int Trie::prefix(std::__cxx11::string)': main.cpp:94:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(++i!=s.size() && x->next[s[i]-'a']!=NULL)///search until end of word or node not allocated ~~~^~~~~~~~~~ main.cpp: In function 'void solve()': main.cpp:125:12: warning: statement has no effect [-Wunused-value] aux; ^