Write a PL/SQL code?

DECLARE
-- Declared variables string, letter, reverse_string where string is the original string. 
string VARCHAR2(10) := 'abccba'; 
letter VARCHAR2(20); 
reverse_string VARCHAR2(10); 
BEGIN
FOR i IN REVERSE 1..LENGTH(string) LOOP 
 letter := SUBSTR(string, i, 1);
 -- concatenate letter to reverse_string variable
 reverse_string := reverse_string ||''||letter; 
END LOOP;
IF reverse_string = string THEN
       dbms_output.Put_line(reverse_string||''||' is palindrome'); 
ELSE
       dbms_output.Put_line(reverse_string ||'' ||' is not palindrome'); 
END IF; 
END;