Compilare: user.cpp: In function ‘int main()’: user.cpp:20:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (ok[s[i]]==false) ^ user.cpp:22:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] ok[s[i]]=true; ^ user.cpp:33:29: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (top<M && ap[s[i]]==false) ^