/in/foo.cc: In function 'int main()':
/in/foo.cc:15:11: warning: array subscript has type 'char' [-Wchar-subscripts]
     d[a[i]]++;
           ^
/in/foo.cc:19:11: warning: array subscript has type 'char' [-Wchar-subscripts]
     e[b[i]]++;
           ^