topic Re: ? on For Next Loops in Libraries & objects

? on For Next Loops

Anonymous — Thu, 07 Sep 2006 19:01:06 GMT

222: !BRICK TIES

FOR dist=0 TO 30' STEP brick_tie
ADDx dist
GOSUB 111

NEXT dist

RETURN

Will this work in an object? It's just putting 1 in and that's it. The brick_tie is a parameter for a length. GOSUB 111 is the actual lines for the brick tie.

Thanks for any help,
Michele

Re: ? on For Next Loops

Anonymous — Thu, 07 Sep 2006 19:07:49 GMT

I forgot to mention this is in the 2D script window - It's not a 3D object only 2D.

Thanks,
Michele

Re: ? on For Next Loops

Anonymous — Thu, 07 Sep 2006 19:51:14 GMT

Michele,
It should work.
Why don't you try it and see.
Del the addx transformations
before return.
Peter Devlin

Re: ? on For Next Loops

Anonymous — Thu, 07 Sep 2006 19:57:31 GMT

I think there was an error in the GOSUB routine (along w/ other errors) but it's working now. A little trial & error goes a long way.

Thanks,
Michele

Re: ? on For Next Loops

Anonymous — Thu, 07 Sep 2006 20:20:07 GMT

It seems that all I do is a lot of trial and error
Peter Devlin

Re: ? on For Next Loops

TomWaltz — Thu, 07 Sep 2006 20:44:33 GMT

Probably not. For/Next works best with integer counters. I am betting you could end up with fractions/decimals pretty easily with this.

I would go with more of a WHILE/DO. like


WHILE dist < 30'-0" DO....

dist = dist + bricktie
ENDWHILE

Re: ? on For Next Loops

Anonymous — Thu, 07 Sep 2006 21:26:07 GMT

Hello Tom,
Could you tell us what happens if
you end up with fractions/decimals.
Until two days ago I thought
for loops could only work with integers
but now I'm not so sure.
Thanks,
Peter Devlin

Re: ? on For Next Loops

TomWaltz — Fri, 08 Sep 2006 12:12:36 GMT

I couldn't say for sure with Archicad, but most programming books I've ever seen tell you to avoid it since you cannot predict how the program will respond.

Re: ? on For Next Loops

Anonymous — Fri, 08 Sep 2006 19:00:31 GMT

Hello Tom,
That was my impression also until, as I said, two days ago.
You mentioned once that you were studying C++.
Does the C++ for loop have the "step" part like GDL ?
It occurs to me that maybe some computer languages
may not have "step" and in that case only integers can be used.
I did a little test using the piece of code using a for loop on
page 1.26 of the GDL Cookbook 3. I tried to force the for loop
to use fractional values and calculate fractional values and
it seemed like there was no problem. The result were always
what you would expect.
Just a few thoughts,
Peter Devlin

Re: ? on For Next Loops

TomWaltz — Fri, 08 Sep 2006 19:13:04 GMT

Peter wrote:
Hello Tom,
That was my impression also until, as I said, two days ago.
You mentioned once that you were studying C++.
Does the C++ for loop have the "step" part like GDL ?
It occurs to me that maybe some computer languages
may not have "step" and in that case only integers can be used.
I did a little test using the piece of code using a for loop on
page 1.26 of the GDL Cookbook 3. I tried to force the for loop
to use fractional values and calculate fractional values and
it seemed like there was no problem. The result were always
what you would expect.
Just a few thoughts,
Peter Devlin

Honestly, I've not used any C++ for almost a year... I think there was, but I cannot say for sure from memory and I'm too lazy to look it up right now 🙂

Re: ? on For Next Loops

Anonymous — Fri, 08 Sep 2006 19:33:14 GMT

Thanks Tom.
I know someone who has a strong computer science background
and I will ask him some of these questions and maybe he will
have some answers.
Thanks,
Peter Devlin

Re: ? on For Next Loops

Oleg — Fri, 08 Sep 2006 20:02:06 GMT

Peter wrote:
Hello Tom,
Does the C++ for loop have the "step" part like GDL ?
Peter Devlin

C++ can use steps of course and more.
A problem may arise for both FOR and WHILE, as result of roundings and comparing floating numbers. ( GDL, C++,...).
Both variants above are IMHO almost equivalent and not quite correct.

IMHO better
FOR dist=0 TO 30 ' + brick_tie / 2 STEP brick_tie

Re: ? on For Next Loops

Anonymous — Fri, 08 Sep 2006 20:29:48 GMT

Hello Oleg,
Great to hear from you.
You say," Both variants above are IMHO almost equivalent
and not quite correct."
Could you elaborate a little please.
How are they both not quite correct ?
Thank you,
Peter Devlin

Re: ? on For Next Loops

Oleg — Fri, 08 Sep 2006 20:50:32 GMT

Peter wrote:
Hello Oleg,
Could you elaborate a little please.
How are they both not quite correct ?
Thank you,
Peter Devlin

Well. Some tests ( AC9 )
What do you think will printed


counter = 0
bstep = 3
FOR dist=0 TO 3 STEP bstep
  counter = counter + 1
NEXT dist
PRINT counter

Imagine there was some calculations.
bstep is same, but what will be printed now


counter = 0
bstep = 0.3/0.1
FOR dist=0 TO 3 STEP bstep
  counter = counter + 1
NEXT dist
PRINT counter

Same for WHILE


counter = 0
bstep = 0.3
dist = 0
WHILE dist < 0.3 DO 
  dist = dist + bstep
  counter = counter + 1
ENDWHILE
PRINT counter

counter = 0
bstep = 1 - 0.7
dist = 0
WHILE dist < 0.3 DO 
  dist = dist + bstep
  counter = counter + 1
ENDWHILE
PRINT counter

The result will depend on actual values and calculations that's mean unstable.

Oleg

Re: ? on For Next Loops

Anonymous — Fri, 08 Sep 2006 21:10:01 GMT

Hello Oleg,
Thank you for your considerable elaboration.
I will have to copy your code into a lib part and
get my head around what is happening.
Thank you,
Peter Devlin

Re: ? on For Next Loops

Anonymous — Fri, 08 Sep 2006 23:42:13 GMT

Hello Oleg,
I did an experiment with your second piece of code.

counter = 0
bstep = 0.3/0.1 !!!=3
FOR dist=0 TO 3 STEP bstep
counter = counter + 1
NEXT dist
PRINT counter !!!! prints 1

PRINT 0.3/0.1 !!!! prints 3

When I change the code to this.

counter = 0
bstep = int(0.3/0.1) !!!=3
FOR dist=0 TO 3 STEP bstep
counter = counter + 1
NEXT dist
PRINT counter !!!! prints 2

It is as though there is a secret fractional part
of the calculation of 0.3/0.1 that is not displayed
in what is printed in PRINT 0.3/0.1 and that there
is a rounding-up in the internal calculations.

How can this be ???
Is PRINT able to lie ?
I wonder how many places PRINT can display.

Peter Devlin

Re: ? on For Next Loops

Oleg — Sat, 09 Sep 2006 07:42:36 GMT

PRINT does not lie. It rounds number to some signs before display ( it seems to 6 signs ).

In any case it needs to be ready, that issues may arise at any comparisons of floating numbers. ( like 0.3 is not equal 1-0.7 )
And if it important in script, use some tricks, like ABS, EPS etc
( It seems there is some guide from GS about that )

FOR loop uses internally comparison too and it may results to unexpected results. Therefore, when a loop uses floating numbers, and not integer, better to use it like
FOR dist=0 TO 3 + bstep / 2 STEP bstep

Oleg

Re: ? on For Next Loops

Anonymous — Sat, 09 Sep 2006 19:13:53 GMT

Hello Oleg,
Yes, this is something that I have only recently come to understand.
Now, all I need to do is remember to put in that little extra to
help AC make it to the finish line.
Thanks Oleg,
Peter Devlin