case inside a cursor

My Version

Oracle8i Enterprise Edition Release 8.1.7.0.0 - Production
PL/SQL Release 8.1.7.0.0 - Production
CORE 8.1.7.0.0 Production
TNS for Solaris: Version 8.1.7.0.0 - Production
NLSRTL Version 3.4.1.0.0 - Production


issue
------

DECLARE
CURSOR s1 IS SELECT '1','2',CASE WHEN 1=2 THEN 1 ELSE 4 END xx FROM dual
BEGIN
FOR c1 IN s1
LOOP
dbms_output.put_line('xx');
END LOOP;
END;

--I AM GETTING THIS ERROR..

ORA-06550: line 2, column 29:
PLS-00103: Encountered the symbol "CASE" when expecting one of the following:

( - + mod null

table avg count current max min prior sql stddev sum variance
execute the forall time timestamp interval date



--The same thing works fine with a simple sql statement on EXECUTE IMMEDIATE..