/in/foo.cc: In function 'int main()':
/in/foo.cc:8:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=1;i<=str.size()-1;i++)
              ~^~~~~~~~~~~~~~
/in/foo.cc:9:11: warning: array subscript has type 'char' [-Wchar-subscripts]
   a[str[i]]++;
           ^