Compilare: user.cpp: In function ‘void query(int, int, int, char)’: user.cpp:23:39: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(H[2*node] & (1LL<<alfa[letter])) query(2*node, lo, mid, letter); ^ user.cpp: In function ‘void update(int, int, int, int, char, bool)’: user.cpp:29:47: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(exists) H[node] = (1LL<<alfa[letter]); ^ user.cpp: In function ‘int main()’: user.cpp:84:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<a.size(); i++) ^ user.cpp:88:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<a.size(); i++) { ^