RE: Having both if/else executing at the same time -- RPG400-L

Tommy,

Your example doesn't compare SELECT/WHEN and IF/ELSEIF.   It doesn't
include an ELSE or ELSEIF.

Your IF/ENDIF groups are intended to execute either TWO of the THREE
options or NONE of them.

If (A) , DO (A stuff) AND (A or B stuff)

If (B) , DO (B stuff) AND (A or B stuff)

IF (not A) and (not B) , DO nothing.

SELECT/WHEN and IF/ELSEIF are functionally the same because both are used
when you want to execute ONLY ONE of the options at most.
Making it the first WHEN means that the (A only stuff) and (B only stuff)
wouldn't execute either.

This would be the SELECT/WHEN equivalent to you IF/ENDIF groups.

select;
   when A;
     // do A stuff
     // do A or B stuff
   when B;
     // do B stuff
     // do A or B stuff
endsl;

James



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  |       Subject:  RE: Having both if/else executing at the same time          
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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;
>
>
> --
> This is the RPG programming on the AS400 / iSeries (RPG400-L) mailing
list
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