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

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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