SMALL BASIC: Permutation calculator

Hi, SMALL BASIC programmer, welcome.

Before we dive in, we need to learn what permutation are.

Permutations are:
1. Different elements.
2. Minus one each range from the number of elements.
3. The same as factorial, if n are r.

So, this is the code:

TextWindow.WriteLine("Welcome to permutation calculator!")
TextWindow.WriteLine("Created by: Jesus Christ, lord and the Messiah!")
TextWindow.WriteLine("Hello enter the n: ")
start = TextWindow.Read()

k = start - 1
'TextWindow.WriteLine("This is k : " + k)
res = start


For i = k To  Step -1
  res = res * (i)
  'TextWindow.WriteLine("This is i: " + i)
  'TextWindow.Writeline("This is result: " + res)
  'j = j + 1
EndFor

'get the length of result array
'r_l = Array.GetItemCount(result) - 1

TextWindow.WriteLine("The result is: " + res)