What is wrong??? (error: numberp:nil)

Hi all.

I'm trying to get minimum and maximum values of x coordinate and y coordinate of a polyline in this code. but it returns this error:

error: bad argument type: numberp: nil

Can anyone tell me what is wrong??

thanks....

 
(DEFUN C:TEST (/ NOVERTEX ENTCNT)
(SETQ SH (SSGET '((0 . "LWPOLYLINE"))))
(SETQ NOVERTEX (CDR (ASSOC 90 (ENTGET (SSNAME SH 0)))))
(SETQ VERTEXLISTX (LIST))
(SETQ VERTEXLISTY (LIST))
(FOREACH A (ENTGET (SSNAME SH 0))
 (IF (= 10 (CAR A))
  (PROGN
   (SETQ VERTEXLISTX
    (APPEND VERTEXLISTX (LIST (CADR A)))
   );_SETQ
   (SETQ VERTEXLISTY
    (APPEND VERTEXLISTY (LIST (CADDR A)))
   );_SETQ
  );_PROGN
 );_IF
);_FOREACH
(SETQ ENTCNT 0)
(WHILE (<= (+ ENTCNT 1) NOVERTEX)
 (PROGN
  (SETQ MINX (MIN (NTH ENTCNT VERTEXLISTX) (NTH (+ ENTCNT 1) VERTEXLISTX)))
  (SETQ MAXX (MAX (NTH ENTCNT VERTEXLISTX) (NTH (+ ENTCNT 1) VERTEXLISTX)))
  (SETQ MINY (MIN (NTH ENTCNT VERTEXLISTY) (NTH (+ ENTCNT 1) VERTEXLISTY)))
  (SETQ MAXY (MAX (NTH ENTCNT VERTEXLISTY) (NTH (+ ENTCNT 1) VERTEXLISTY)))
  (SETQ ENTCNT (+ ENTCNT 1))
 );_PROGN
);_WHILE
);_DEFUN

error: bad argument type: numberp: nil

This happens when using (nth ) when the is outside the scope of a list

Sample

(setq tempList (list "abc" "def" "ghi"))

(nth 4 tempList)

On the final loop

 (WHILE (<= (+ ENTCNT 1) NOVERTEX)

the error arrises at

   (SETQ MINX (MIN (NTH ENTCNT VERTEXLISTX) [color="Red"](NTH (+ ENTCNT 1) VERTEXLISTX)[/color]))

For an alternative method of sorting the points

Swap

(SETQ ENTCNT 0)
(WHILE (<= (+ ENTCNT 1) NOVERTEX)
 (PROGN
  (SETQ MINX (MIN (NTH ENTCNT VERTEXLISTX) (NTH (+ ENTCNT 1) VERTEXLISTX)))
  (SETQ MAXX (MAX (NTH ENTCNT VERTEXLISTX) (NTH (+ ENTCNT 1) VERTEXLISTX)))
  (SETQ MINY (MIN (NTH ENTCNT VERTEXLISTY) (NTH (+ ENTCNT 1) VERTEXLISTY)))
  (SETQ MAXY (MAX (NTH ENTCNT VERTEXLISTY) (NTH (+ ENTCNT 1) VERTEXLISTY)))
  (SETQ ENTCNT (+ ENTCNT 1))
 );_PROGN
);_WHILE

For

 
  (SETQ MINX (apply 'min VERTEXLISTX))
  (SETQ MAXX (apply 'max VERTEXLISTX))
  (SETQ MINY (apply 'min VERTEXLISTy))
  (SETQ MAXY (apply 'max VERTEXLISTy))

Dear jammie,

So thanks for your complete guildance.

Your alternative code is great.

But there is one question:

By increasing "entcnt" to 4, shouldn't the loop stop when (novertex=4)???

By increasing "entcnt" to 4, shouldn't the loop stop when (novertex=4)???

Yes,

The While loop stops when

(

BUT, on the last run through, when you are dealing with the last vertex ; you use this

(nth (+ ENTCNT 1) VERTEXLISTX)

effectively asking for the index AFTER the last one ...

Just for comparison, perhaps have a look at something like this

 

(defun c:doit (/ sh ll ur)
 (vl-load-com)
 (setq SH (ssget '((0 . "LWPOLYLINE"))))
 (vla-getboundingbox
   (vlax-ename->vla-object (ssname SH 0))
   'll
   'ur
 )
 (setq ll (vlax-safearray->list ll)
       ur (vlax-safearray->list ur)
 )
 (alert (strcat
          "LowerLeft : "
          (vl-prin1-to-string ll)
          "\nUpperRight : "
          (vl-prin1-to-string ur)
        )
 )

OK.

I'm so thankful about your description and altenative code. It is perfect and has a few arguman vs. my code.

It is so faster by using activex functions.

I hope that i learn this method as soon as possible.