Re: FOR loop limit

There may be a good reason, although idle speculation, since we do not have the designers to ask why.

Languages like C are so directly working with pointers that using offsets makes sense - hence, the reason to start with 0.

Languages like RPG deal with more concrete things - 4 quarters in a year, 12 months in a year (13 under another accounting methodology). So we think in more typical ways - quarter 1 is index 1, etc. It seems that RPG has, for the longest time, insulated us from having to deal with pointers - still does, unless we really try potentially to shoot ourselves in the foot.

Anyhow, as I said, this is all speculation. And besides, you get to do this in RPG, too, if you want. You can do the same with arrays in VB - just base you array on whatever is practical - maybe the human perception of elements has a range from 12 to 27 - hey, don't ask me for a real real-world example.

So write it as

for x = 0 to 2

if you want and do the increment. Or do it as the language is constructed.

Finally, unless you are like me, why ask why!!

Regards
Vern

David FOXWELL wrote:

Why don't we start at 0 like in other languages?

Eg,

For (int i=0 ; numberloops-1 ; i++)
Index= i + 1;


EndFor

What is the value of Index when the loop ends?





-----Message d'origine-----
De : rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] De la part de Rory Hewitt
Envoyé : jeudi 29 janvier 2009 18:44
À : RPG programming on the IBM i / System i
Objet : Re: FOR loop limit

Jeff,

It's always been a pain like this. I assume there's some backwards-compatibility issue that made it work like this:

for x = 1 to 3;
...do something
endfor;

After the loop, x is 4, *not* 3.

If you step through in debug, you can see how it stops on the endfor after the 3rd time and then stops again on the endfor before moving on. It's documented in the RPG manual, but still it seems screwy to me. Couldn't they have added processing to not increment the counter after the last one (or to decrement it back again)?

Rory

On Thu, Jan 29, 2009 at 9:32 AM, Jeff Crosby <jlcrosby@xxxxxxxxxxxxxxxx>wrote:

I learned something new today.

Take the following program:

D x S 3P 0
D y S 3P 0

/free

*INLR = *On;
Y = 999;

For X = 1 To Y By 1;
EndFor;

Return;

/end-free


The program bombs with the dreaded "Message . . . . : The target for a
numeric operation is too small to hold the result (C G D F)."

I guess when the endfor is reached the last time through, it attempts
to set the value of x to 1,000.

Live and learn.

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