not or null who help

hi, couple of quest. this routine is supposed to check 2 endpoints of diff lines to see if they lie on the same point.

(defun c:ce ()
(setvar "cmdecho" 0)

(while (not (setq ent (entsel "\nPick line 1 (near endpoint)"))))
;quest. if the "not" returns true if nothing's selected then y DOESN'T it quit the loop when nothing's selected?
(setq z (car ent))
(redraw z 3)
(setq a (cdr ent)
b (car a)
end1 (osnap b "endp"))
; the following is where the prob is. if nothing's selected it's supposed to go to nothing selected.
; neither of the conditions work

(while (or (equal z (setq ent1 (entsel "\nPick line 2 (near endpoint)")) (car ent1)) (not ent1)) ;or
(alert
(cond ((null ent1) "Nothing Selected")
(T "You've Picked the same Line")
);cond
) ;alert
) ;while


(setq a1 (cdr ent1)
b1 (car a1)
end2 (osnap b1 "endp"))

(if
(equal end1 end2)
(print "Endpoints are Equal")
(progn
(setq east (rtos (- (car end1) (car end2)) 2 4)
north (rtos (- (cadr end1) (cadr end2)) 2 4)
de (strcat "Diff E=" east)
dn (strcat "Diff N=" north))
(alert (strcat "Endpoints are Not Equal!!"
"\n"de
"\n"dn))))
(redraw z 4)



(princ)
)

TIA, Shawn

 

(while (not (setq ent (entsel "\nPick line 1 (near endpoint)"))))

it quit the loop when nothing's selected?
***Because while continues as long as the test results in a non-nil value
(including true).

"while continues" does that mean that it exits the loop and continues to the next line? Or continues looping?
If i understand correctly if I select nothing it will return a nil which "not" will return a "T" value and satisfy the loop; thereby continueing on with the remainder of the program. But this isn't what happens. If i click nothing it still asks to select line one. Don't get me wrong it acts correctly, I just don't understand why.

The second loop still doesn't work.

Shawn

 

Hi Shawn, see inline comments. HTH
--
James Allen, EIT
Malicoat-Winslow Engineers, P.C.
Columbia, MO

diff lines to see if they lie on the same point.

it quit the loop when nothing's selected?
***Because while continues as long as the test results in a non-nil value
(including true).

supposed to go to nothing selected.

***I haven't tested to see if there is more, but it looks like the whole
setq statement should be in the (car ), like
***(equal z (car (setq ent1 (entsel "\nPick line 2 (near endpoint)"))))

 

(while
(not ;--------------------------------------while I haven't picked
anything....
(setq ent ;---------------------------------keep trying to pick
something....
(entsel "\nPick line 1 (near endpoint)")
)
)
;------------------------------------------once I have picked something,
i'm done in the loop
)
;------------------------------------------and continue with the rest of
the program

the next line?

no, continue doesn't mean exit the loop, it means continue the loop....

continues looping

in the case of the while function, satisfaction means keep looping
"Keep looping while this is true"
"as long as I keep getting satisfied by something I'll keep doing it"


read the description of the while function in the help files, maybe that
will clear it up

it will continue looping as long as it's test is true
which in your case is as long as you haven't picked something
in other words your loop says,
while I haven't picked something, keep trying to pick something
as soon as I *have* picked something, then get out of the loop and
continue with the rest of the program

what happens. If i click nothing it still asks to > select line one. Don't
get me wrong it acts correctly, I just don't understand why.
hope that clarifys it
Mark

 

while trUE, continUE

The second loop doesn’t work because your comparing 3 things with the equal. This works:
(or (equal Z (setq ENT1 (car (entsel "\nPick line 2 (near endpoint)"))))
(not ENT1)
) ;or

But if your only checking lines, don’t you want to make sure ENT is a line? Using osnap to get an endpoint is flaky because you could get either end depending on which side of middle you pick. You need to look into (entget (car (entsel)))

 

Thnx so much guys, I really appreciate your time.

Shawn.