/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=0;i<strlen(s);i++)
              ~^~~~~~~~~~
/in/foo.cc:9:9: warning: array subscript has type 'char' [-Wchar-subscripts]
   a[s[i]]++;
         ^
/in/foo.cc:12:9: warning: array subscript has type 'char' [-Wchar-subscripts]
   if(a[i]!=0)cout<<i; 
         ^
/in/foo.cc:17:9: warning: array subscript has type 'char' [-Wchar-subscripts]
   if(a[i]!=0)cout<<a[i];
         ^
/in/foo.cc:17:23: warning: array subscript has type 'char' [-Wchar-subscripts]
   if(a[i]!=0)cout<<a[i];
                       ^