SQL> declare
  2    achar char(1) := '&achar';
  3    description varchar2(20);
  4  begin
  5    description := 
  6       case achar
  7          when 'A' then 'Excellent'
  8          when 'B' then 'Very Good'
  9          when 'C' then 'Good'
 10          when 'D' then 'Fair'
 11          when 'F' then 'Poor'
 12          else 'No such grade'
 13       end;
 14     dbms_output.put_line('The description was ' || description);
 15  end;
 16  /
Enter value for achar: B
old   2:   achar char(1) := '&achar';
new   2:   achar char(1) := 'B';
The description was Very Good

PL/SQL procedure successfully completed.

SQL>