LISTING 2: The dbo.fn_cast9() Function Implemented with Loops

CREATE FUNCTION dbo.fn_cast9(@num AS int) RETURNS int
AS
BEGIN

  IF @num < 0 OR @num IS NULL
    RETURN NULL
    
   DECLARE @curnum AS int, @result AS int
   
   SET @curnum = @num
  SET @result = @num

  WHILE @result >= 10
  BEGIN
    SET @result = 0
    WHILE @curnum > 0
    BEGIN
      SET @result = @result + @curnum % 10
      SET @curnum = @curnum / 10
    END
    SET @curnum = @result
  END

  RETURN @num * 10 + @result
END