Write PL/SQL program?

DECLARE
-- declare necessary variables 
   -- num represents the given number
   -- number_to_word represents the word format of the number
   -- str, len and digit are the intermediate variables used for program execution
num   INTEGER; 
number_to_word VARCHAR2(100); 
digit_str   VARCHAR2(100); 
len   INTEGER; 
digit   INTEGER; 
BEGIN
   num := 123456; 
   len := LENGTH(num); 
   dbms_output.PUT_LINE('Input: ' ||num);
   -- Iterate through the number one by one
   FOR i IN 1..len LOOP 
       digit := SUBSTR(num, i, 1);
       -- Using DECODE, get the str representation of the digit
       SELECT Decode(digit, 0, 'Zero ', 
                       1, 'One ', 
                       2, 'Two ', 
                       3, 'Three ', 
                       4, 'Four ', 
                       5, 'Five ', 
                       6, 'Six ', 
                       7, 'Seven ', 
                       8, 'Eight ', 
                       9, 'Nine ') 
       INTO digit_str 
       FROM dual;
       -- Append the str representation of digit to final result.
       number_to_word := number_to_word || digit_str; 
   END LOOP;
   dbms_output.PUT_LINE('Output: ' ||number_to_word); 
END;