How do you get to Keprekar's constant when you start with a one digit number?

How do you get to Keprekar's constant when you start with a one digit number? As far as l know there are 2 values considered as Keprekar's constants 495 (if you start with a 3 digit number) or 6174 if you start with a 4 digit number. I am working on a function to count how many steps are needed to take a number and get it to Keprekars constant using Keprekar's routine described below. I saw a Matlab cody challenge linked here( https://www.mathworks.com/matlabcentral/cody/groups/2/problems/68 ) where one of the test cases says you actually can get to Keprekars constant when you start with one digit.

Keprekar's Routine:

1. Take any four-digit number, using at least two different digits (leading zeros are allowed).
2. Arrange the digits in descending and then in ascending order to get two four-digit numbers, adding leading zeros if necessary.
3. Subtract the smaller number from the bigger number.
4. Go back to step 2 and repeat

Source for Keprekars Routine Description:

https://en.wikipedia.org/wiki/6174_%28number%29

Answer 1

[Walter Roberson]

new = randi(9)

new = 3

while true
  old = new
  new = sprintf('%04d', old)
  new = str2num(sort(new, 'descend')) - str2num(sort(new,'ascend'))
  if new == old; break; end
end

old = 3

new = '0003'

new = 2997

old = 2997

new = '2997'

new = 7173

old = 7173

new = '7173'

new = 6354

old = 6354

new = '6354'

new = 3087

old = 3087

new = '3087'

new = 8352

old = 8352

new = '8352'

new = 6174

old = 6174

new = '6174'

new = 6174

new

new = 6174

[Ntandoyakhe Tshuma]

Oh I see. I thought about adding zeros to it but my concern was that in the case of x being 1 it would eventually just get to zero.

x = 1

asc = 0001

dsc = 1000

dsc - asc = 999

dsc = 999

asc =999

dsc - asc = 0

but with the way your code is formatted the value would be 0999 allowing the code to keep running. Thank you.

[Walter Roberson]

Note: the code could be written more efficiently. The point was not to be as efficient as possibe: the point was to show it could be done.