Just testing you

[john.uhden]

What's wrong with this code?

(defun factorial (n / product)
  (setq i 0 product 1)
  (repeat n
    (setq i (1+ i) product (* i product))
  )
  product
)

[pbejse]

---

@john.uhden wrote:

What's wrong with this code?

---

It works as expected. <--- it does have a limit,  like most things  in lisp that deals with integers

(defun factorial (n / product)
  (setq i 0.0 product 1)
  (repeat n
    (setq i (1+ i) product (* i product))
  )
  (fix product)
)

[john.uhden]

@pbejse
You sorta beat around the bush with that answer, but You deserve an A+ for
demonstrating that you totally understood. Yes, I saw that you changed one
of the operands to a 'REAL.
Seems like even long integers have their limit in AutoLisp.

Anyone else?

[hak_vz]

(defun factorial (n / product)
  (setq i 0 product 1.0)
  (repeat n
    (setq i (1+ i) product (* i product))
  )
  product
)

Yes. Integers have limits in autolisp too.

[dbroad]

IMO, the ideal factorial function should be recursive, not iterative. It is the paradigm for a recursive definition. If the user wants a real result, then, he should provide a real argument, else, he should accept the limitations of integers.

(defun factorial (n)
  (if (= n 1) 1
  (* n (factorial (1- n)))))

Since its only defined for positive whole numbers(integers in real math), that is all you should need to do.

[john.uhden]

@Anonymous
Whoa! I ain't never been too good with recursion.
Gotta study that and probably give you an A++.
I will do a time test, of course.

[dbroad]

Thanks but time tests are probably irrelevant.  Factorial results increase faster than exponentially.  You probably won't want a number larger than 64 as input.

[john.uhden]

Next question:

What's the largest integer that AutoLisp can handle?

[Jeff_M]

---

@john.uhden wrote:

Next question:

What's the largest integer that AutoLisp can handle?

---

2147483647

https://help.autodesk.com/view/ACD/2015/ENU/?guid=GUID-EF6114FC-F1E4-4C71-91CC-07D01E6C8ABB

[john.uhden]

Hi, Jeff.
Well done, even though you cheated.
Didja notice it's one shy of (expt 2 31)?
which turns negative and (abs) can do nothing to it.

[martti.halminen]

This one also works in Common Lisp:

CLO 17 > (factorial 92)
12438414054641307255475324325873553077577991715875414356840239582938137710983519518443046123837041347353107486982656753664000000000000000000000

- The trick here is that CL has bignums when it runs out of space on integers.

- Also demonstrates the problem with recursive functions, on 93 I get:

Stack overflow (stack size 15998).
[Condition of type CONDITIONS:STACK-OVERFLOW]

Restarts:
0: [CONTINUE] Extend stack by 50%.
1: [ABORT] Return to top loop level 0.
2: [ABORT] Quit process.

So if I really needed larger ones, I'd need to change to another algorithm (iterative or  recursive with memoizing or using an accumulator).

--