RE: Having both if/else executing at the same time

[AGlauser@xxxxxxxxxxxx]

Sorry, I wasn't clear.  The select/when (with the 'leave' in it) is what I 
*want* to do when I use select.  I realize that in RPG, the multiple 
if/then that I have is different that select/when, and if/elseif is the 
same as select/when.

What I was saying is that I use if/elseif because in the first languages I 
used, the case structure acted more like multiple if/endifs, and I think I 
like that behaviour better.

Thanks for a good,clear explanation nonetheless,
Adam


rpg400-l-bounces+aglauser=erbgroup.com@xxxxxxxxxxxx wrote on 25/05/2006 
03:48:12 PM:

> The only significant difference that I am aware of between if/elseif &
> select/when is this:
> 
> In This example, each if is evaluated at run-time:
>  if (A)
>   // do A stuff
> endif;
> 
> if (B);
>   // do B stuff
> endif;
> 
> if ((A OR B));
>   // do A or B stuff
> endif;
> 
> 
> 
> With select the when is evaluated until it finds the first match & skips
> the rest of the checks
> 
> So in this example the "when A or B" would never be execute since an
> matching true expression has already occurred.
> 
> select;
>    when A;
>       // do A stuff
> 
>    when B;
>       // do B stuff
>       leave;
>    when A or B;
>      //do A or B stuff
> 
>    other;
>       // some sort of error
> 
> endsl;
> 
> 
> Thanks,
> Tommy Holden
> 
> 
> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx
> [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of
> AGlauser@xxxxxxxxxxxx
> Sent: Thursday, May 25, 2006 2:36 PM
> To: RPG programming on the AS400 / iSeries
> Subject: RE: Having both if/else executing at the same time
> 
> Willie,
> 
> Have you stepped through the code?  Any new information to pass on?
> 
> 
> Joe,
> 
> I'm interested in your reasons for using select/when over if/elseif.  I 
> think I prefer if/elseif only because I learned about them first, and to
> 
> me case-like statements should fall through like they do in C.  It seems
> 
> redundant to me to have both structures behave identically, and awkward
> to 
> have to do:
> 
> if (A)
>   // do A stuff
> endif;
> 
> if (B);
>   // do B stuff
> endif;
> 
> if (NOT (A OR B));
>   // some sort of error
> endif;
> 
> when what I'd like to do is:
> 
> select;
>    when A;
>       // do A stuff
> 
>    when B;
>       // do B stuff
>       leave;
> 
>    other;
>       // some sort of error
> 
> endsl;
> 
> I realize that you're not advocating one method over the other, but I've
> 
> heard people say that it is 'better' to use select/when instead of 
> if/elseif, but they never provide any good reasons.  Do you have any, or
> 
> does it just feel more natural the way if/elseif does to me?
> 
> Adam
> 
> 
> rpg400-l-bounces@xxxxxxxxxxxx wrote on 25/05/2006 02:53:47 PM:
> 
> > Actually, the original code simply selected among three mutually 
> exclusive
> > conditions.  Using an ELSEIF doesn't change the outcome at all.
> > 
> > IF CondA;
> >   DoA;
> > ELSE;
> >   IF CondB;
> >     DoB;
> >   ELSE;
> >     DoC;
> >   ENDIF;
> > ENDIF;
> > 
> > Is functionally equivalent to:
> > 
> > IF CondA;
> >   DoA;
> > ELSEIF CondB;
> >   DoB;
> > ELSE;
> >   DoC;
> > ENDIF;
> > 
> > The ELSEIF just removes the second "endif" (which you accidentally
> left 
> in
> > your post, Bob, LOL!).  This is also functionally equivalent to:
> > 
> > SELECT;
> >   WHEN CondA;
> >     DoA;
> >   WHEN CondB;
> >     DoB;
> >   OTHER;
> >     DoC;
> > ENDSL;
> > 
> > Nowadays I tend towards the third form if there are more than two 
> mutually
> > exclusive conditions.
> > 
> > It should be noted that the three conditions being selected among are
> > (CondA), ((NOT CondA) and (CondB)), and finally ((NOT CondA) and (NOT
> > CondB)).  That is, even if both CondA and CondB are true, only the
> first
> > branch of the code will be executed.
> > 
> > Joe
> > 
> > 
> > > From: Bob Cozzi
> > > 
> > > ELSE and IF are two statements. In your code the only time the
> second 
> IF
> > > will be
> > > performed is when the first IF fails. Why? Because the first ELSE is
> 
> only
> > > going
> > > to be run if the first IF fails. Otherwise it'll jump to the ENDIF
> > > statements.
> > > I think what you really mean to have is ELSEIF not "ELSE" and "IF".
> > > Replace the ELSE and IF with ELSEIF, and then take a look as this 
> page:
> > > 
> > > www.rpgiv.com/blueribbon.html
> > > 
> > >   if %len(%trim(APIErrMsg)) > 0;
> > >      W#ERFL = *ON;
> > >      W#MSDT = 'Error #' + APIErrMsg + ' receiving data from ' +
> > >               'data queue.  Detail:  ' + APIErrDta;
> > >    elseif %trim(itmInfo) = '';
> > >       W#ERFL = *ON;
> > >       W#MSDT = 'Invalid data received from data queue: ' +
> > >             itmInfo ;
> > >    else;
> > >        uMATNO = jMATNO;
> > >        uSIZE = jSIZE;
> > >        uTEMPER = jTEMPER;
> > >        uINSUL = jINSUL;
> > >        uTENSIL = jTENSIL;
> > >    endif;
> > >    endif;
> > 
> > 
> > -- 
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> list
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> > 
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