RE: dim lights?

[CWilt@xxxxxxxxxxxx]

No he isn't saying the position of the and makes a difference.

What makes a difference is the order of the expressions.

imagine pos = 53 and that InputMAS is defined dim(52)

dow (InputMAS(pos) <> ';') and pos < 52
    //checking InputMAS(53)<> ';' gives array out of bounds, it never gets
to evaluate pos < 52 

dow pos < 52 and (InputMAS(pos) <> ';')
    // since pos < 53 is false, the whole statement is false 
    //   InputMAS(53) is not evaluated.

This is know as 'short-circuit evaluation'.  Quite common in all modern
languages.
Basically, when evaluating a bunch of expressions connected via 'and' and
you hit one that is false, the whole statement is false and you don't need
to look at the rest.  Works the same for a bunch of statements connected via
'or' except you are looking for the first true.

HTH,
Charles


> -----Original Message-----
> From: Gerald Magnuson [mailto:gmagnuson@xxxxxxxxxxx]
> Sent: Thursday, March 25, 2004 12:08 PM
> To: RPG programming on the AS400 / iSeries
> Subject: Re: dim lights?
> 
> 
> Hans,
> Are you saying it makes a difference
> if we have the "and" on the top line,
> or on the next line?
> Could you explain why that is?
> 
> Hans Boldt (boldt@xxxxxxxxxx) wrote:
> >
> > Ted Barry wrote:
> > > What is wrong with this statement?:
> > >
> > > dow       (InputMAD(pos) <> ';') and
> > >           pos < 52
> > > eval      pos = pos + 1
> > > enddo
> > >
> > > Total dims are 52, so why am I getting an array index error?
> > >
> >
> > Rewrite it as:
> >
> > --------------------------------------
> > dow        pos < 52
> >             and (InputMAD(pos) <> ';')
> > eval      pos = pos + 1
> > enddo
> > --------------------------------------
> >
> > and try again. If the first condition is not true, the 
> second won't be
> > evaluated.
> >
> > Cheers! Hans
> >
> > _______________________________________________
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> >
> 
> --
> Gerald Magnuson
> The Knapheide Manufacturing Company
> Quincy Illinois
> 
> 
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