EXCEPTION  -- exception handlers begin

-- Only one of the WHEN blocks is executed.

   WHEN ZERO_DIVIDE THEN  -- handles 'division by zero' error
      dbms_output.put_line('Company must have had zero earnings.');
      pe_ratio := null;

   WHEN OTHERS THEN  -- handles all other errors
      dbms_output.put_line('Some other kind of error occurred.');
      pe_ratio := null;