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"ingo" <ing### [at] home nl> wrote in message
news:8FA4E57A0seed7@204.213.191.228...
| python it indeed is all (more or less) automatic.
|
| while i in range(25):
| while j in range(25):
| do some things here inside the loops
|
| continue program outside the loop
That looks awfully easy. Why the word "in" though? Just so you don't think
it's too simple?
Bob
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In article <8FA4E57A0seed7@204.213.191.228>, ing### [at] homenl (ingo)
wrote:
> Think about it with an absolute non-programmer mind.
Easier said than done.
> When I first encouterd a loop, it took men an hour to realize that I had
> to do the incrementing myself. I expected it to be automatic.
This is done for flexibility and ease of coding...a variable is just a
variable, whether you use it as a counter or not, how is POV supposed to
know it needs to be incremented when the loop ends? Also, there are
times when you want to increment the loop by a different amount, and
times when you don't even want to use an incrementing variable for
control. Loops aren't only used for making several copies of an object.
> It took me a day to figure out I had to reset the counter of the inner
> loop myself. For me it seemed very logical that once I had gone through
> the loop the counter would not exist anymore until the loop was enterd
> again.
This could make sense if you created the variable inside the outer loop
in many other languages, but if you create it outside both loops, why
would you expect it to be destroyed when the outer one loops back to
it's start?
Anyway, POV seems to only have variables local to files and macros. With
a separate keyword for modifying variables, like what my #set patch
implements, it would be possible to use variables local to any block,
like #if statements and #while loops, but I don't expect that to happen
for a while, if ever.
--
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/
<><
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Ok, I added an entry about the while loops and made a page about it:
http://iki.fi/warp/povVFAQ/whileloops.html
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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Bob Hughes wrote:
>That looks awfully easy.
That why I like it.
>Why the word "in" though? Just so you don't
>think it's too simple?
Don't ask me...
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
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Warp wrote:
> Ok, I added an entry about the while loops and made a page about it:
>
>http://iki.fi/warp/povVFAQ/whileloops.html
>
excellent!
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
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Chris Huff wrote:
<snip>
>it would be possible to use variables local to any block,
>like #if statements and #while loops, but I don't expect that to happen
>for a while, if ever.
Neither do I, nor do I want it. It was just to illustrate how "illogic" a
total non-programmer can think(me, two years ago, after only two days
playing with POV).
Compare it to chess. You can learn anybody the moves each piece can make,
but he'll only be able to play chess after he grasps the concept behind
the game.
Ingo
--
Photography: http://members.home.nl/ingoogni/
Pov-Ray : http://members.home.nl/seed7/
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On 3 Sep 2000 16:10:41 -0400, ingo wrote:
>Think about it with an absolute non-programmer mind.
>When I first encouterd a loop, it took men an hour to realize that I had
>to do the incrementing myself. I expected it to be automatic.
>It took me a day to figure out I had to reset the counter of the inner
>loop myself. For me it seemed very logical that once I had gone through
>the loop the counter would not exist anymore until the loop was enterd
>again.
In most languages this is the difference between a while loop and a for
loop. The while loop is repeated while a certain condition is true. The
for loop is repeated for a set of values.
For example, in
#local a = 0;
#while (a < 20)
...
#end
You can do everything with a inside the loop, as long as you stay below
20. You don't just have to increase it by 1 with every cycle. You can
increase it by 0.1, by a random value, you can decrease it again, or you
can compute it as a function of some other variable.
On the other hand, Pascal (for example) has a for loop:
var i: integer;
begin
i := 5;
for i := 1 to 20
do
println(i);
done
println(i); { ??? }
end;
will print the values from 1 to 20. No need to increment manually,
because the loop always increments the count by 1. In fact you are not
allowed to assign a new value to i inside the loop, and it isn't
specified what the println after the loop will print. 5, 20, or 21 would
be values you could expect (if you know a little bit about how a pascal
compiler works), but it could also be some completely random value.
So the for loop is simpler, but less flexible. Because you can always
rewrite a for loop as a while loop, but not vice versa, Povray only has
a while loop.
hp
--
_ | Peter J. Holzer | Nicht an Tueren mangelt es,
|_|_) | Sysadmin WSR | sondern an der Einrichtung (aka Content).
| | | hjp### [at] wsracat | -- Ale### [at] univieacat
__/ | http://www.hjp.at/ | zum Thema Portale in at.linux
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I just added more stuff at the end of the document, if someone is interested.
--
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/
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Yours looks more in-depth but Sonya Roberts has a #while tutorial
at the Rendering Times...
http://www.spake.org/rtimes/article/povindx.htm
--
Phil
...coffee?...yes please! extra sugar,extra cream...Thank you.
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Phil Clute wrote:
>
> Yours looks more in-depth but Sonya Roberts has a #while tutorial
> at the Rendering Times...
> http://www.spake.org/rtimes/article/povindx.htm
Were it not for that tutorial I never would have understood #while loops.
--
Ken Tyler - 1400+ POV-Ray, Graphics, 3D Rendering, and Raytracing Links:
http://home.pacbell.net/tylereng/index.html http://www.povray.org/links/
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