Compilare: user.cpp:23:18: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] char index = NULL; ^ user.cpp: In member function ‘void ahtree::insert(char*)’: user.cpp:32:24: warning: array subscript has type ‘char’ [-Wchar-subscripts] imply[index].push_back(cindex); ^ user.cpp: In function ‘void fix_failure()’: user.cpp:63:34: warning: array subscript has type ‘char’ [-Wchar-subscripts] imply[now ->index].push_back(now ->failure ->index); ^ user.cpp: In function ‘void search()’: user.cpp:98:34: warning: array subscript has type ‘char’ [-Wchar-subscripts] ++ nr_app[now ->index]; ^ user.cpp:110:42: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < imply[i].size(); j ++){ ^ user.cpp:111:31: warning: array subscript has type ‘char’ [-Wchar-subscripts] nr_app[imply[i][j]] += nr_app[i]; ^