/in/foo.cc: In function 'int main()':
/in/foo.cc:10:24: warning: array subscript has type 'char' [-Wchar-subscripts]
   if (isalpha(ch)) a[ch] ++;
                        ^
/in/foo.cc:16:16: warning: iteration 349 invokes undefined behavior [-Waggressive-loop-optimizations]
   if (Max < a[i]) pos = i, Max = a[i];
             ~~~^
/in/foo.cc:15:20: note: within this loop
  for (int i = 1; i <= 1000; i++)
                  ~~^~~~~~~