Re: OPEN in RPGIII

["Mark S. Waterbury" <mark.s.waterbury@xxxxxxx>]

Hi, Jerry:

Thanks for those clarifications.

In the early 1980s, they were teaching RPG II on an IBM System/34 at St. 
Petersburg Junior College in Clearwater, Florida, and the instructors 
there had come up with some very clever ways to teach "structured 
programming" using only what RPG II provided at that time. The technique 
relied on heavy use of EXSR. So, for example, and IF-ELSE-END logic 
block might look somethling like this:

           FLDA  COMP FLDB         010203
  01             EXSR THEN01
  0203           EXSR ELSE01

and so on. The statements to be executed in the "then" would be 
contained in a BEGSR and ENDSR with the name "THEN01" (in this case), 
and the statements for the "else" would be in another subroutine with 
the name "ELSE01", and so on.  Of course, you could also try to make up 
more "meaningful" names instead of "THENnn" and "ELSEnn", within the 
limits of six-character names... you get the idea...?

Also, a DO-WHILE it looked something like this:

         WHILE1  TAG
           FLDA  COMP FLDB         01
  01             EXSR WHL01
  01             GOTO WHILE1

And a DO-UNTIL it looked something like this:

         UNTIL1  TAG
                 EXSR UTL01
           FLDA  COMP FLDB         01
 N01             GOTO UNTIL1

You get the idea... Also, if the number of statements to be executed in 
the "body" of the loop was small, they might be included in-line, rather 
than using an EXSR as shown above.

They also encouraged a very "modular" style of coding, where the 
"main-line CALCs" were usually just a sequence of EXSRs, and all of the 
actual logic was contained inside one or more subroutines.

Not too bad, considering the "state of the art" in System/34 RPG II in 
the late '70s and early '80s ...

That's about all I can remember from those days.

Mark S. Waterbury

> Jerry Adams wrote:
> Mark,
>
> There were no structured op-codes (IF, DO) on the S/34 - except through Schuette's (sic) RPG II 1/2.
>
> They were added to the /36 when the Advanced/36 models came out (SSP 7?), but they were somewhat crippled.  CAB was never part of IBM's RPG II compilers.
>
> Jerry C. Adams
> IBM System i Programmer/Analyst
> --
> B&W Wholesale
> office: 615-995-7024
> email:  jerry@xxxxxxxxxxxxxxx
>
>
> -----Original Message-----
> From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Mark S. Waterbury
> Sent: Thursday, March 04, 2010 8:13 AM
> To: RPG programming on the IBM i / System i
> Subject: Re: OPEN in RPGIII
>
> Hi, Terry:
>
> IBM System/3 RPG II had only COMP, indicators, GOTO and TAG, and EXSR, 
> BEGSR and ENDSR (for "control flow").
>
> With the IBM System/34, IBM added "structured programming" opcodes 
> (still calling it RPG II):
>
>     IF - ELSE - END
>     DOWxx   - END, DOUxx - END, DO - END
>     CASxx
>
> CALL and PARM were added with Systen/36 Release 6 (VASP).
>
> I think CABxx was introduced with System/38 RPG III.
>
> (Anyone else remember those details any better?)
>
> HTH,
>
> Mark S. Waterbury
>
>  > Terrence Enger wrote:
>   
> > Hmm, this is a real memory test for me, but are you sure that RPG II had
> > the CABxx and CASxx opcodes?  I only remember these from RPG III.
> >
> > CVTRPGSRC, of course, does not claim to work for RPG II.
> >
> > Cheers,
> > Terry.
> >
> >
> >   
> >