/in/foo.cc: In function 'int main()':
/in/foo.cc:28:34: warning: array subscript has type 'char' [-Wchar-subscripts]
   for(int i=0;i<len;++i) ++a[s[i]].num;
                                  ^
/in/foo.cc:29:40: warning: array subscript has type 'char' [-Wchar-subscripts]
   for(char i='A';i<='Z';++i) q.push(a[i]);
                                        ^
/in/foo.cc:30:14: warning: unused variable 'f3' [-Wunused-variable]
   node f1,f2,f3;
              ^~