Compilare: main.cpp: In function 'void _insert(std::__cxx11::string&)': main.cpp:24:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while(i < s.size()) { ~~^~~~~~~~~~ main.cpp:26:23: warning: array subscript has type 'char' [-Wchar-subscripts] if(curr->nxt[c] == 0) { ^ main.cpp:27:24: warning: array subscript has type 'char' [-Wchar-subscripts] curr->nxt[c] = new Node(); ^ main.cpp:29:27: warning: array subscript has type 'char' [-Wchar-subscripts] curr = curr->nxt[c]; ^ main.cpp: In function 'void _count(int, int)': main.cpp:42:23: warning: array subscript has type 'char' [-Wchar-subscripts] if(curr->nxt[c]) { ^ main.cpp:43:31: warning: array subscript has type 'char' [-Wchar-subscripts] curr = curr->nxt[c]; ^ main.cpp: In function 'int main()': main.cpp:65:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < S.size(); ++i) ~~^~~~~~~~~~