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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] wsr acat | -- 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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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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