Re: Back with recursion in COBOL again!

I personally would prefer this solution with service program before the 
solution with tle LOCAL-STORAGE SECTION from  ILE COBOL Programmers Guide. 

The service program is here needed, because without the service program we 
could not realise calling with returning a value, i.e.
CALL PROCEDURE ... RETURNING INTO...
Only the ILE-COBOL procedure can return a value and the procedure needs to 
be placed in a service program.

On the one side using the procedures and service programs makes possible 
porcedures/functions with local variables,
which brings to the COBOL-programming more elegancy and makes possible 
to solve e.g. such recursion problems at analogical way as to solve it in 
any other programming language like Python, C, Pascal ...
 
On the other side however, using the procedures and service programs needs 
more effort to create the program: 
First you need to create the modules with CRTCBLMOD, 
then to create or update your service program with CRTSRVPGM or UPDSRVPGM 
and finally to link the entry module with the service program together in 
a runable program with CRTPGM. 

:-)

Regards

Roman




"Shijith Chand" <shijith_c@xxxxxxxxxxx> 
Sent by: cobol400-l-bounces@xxxxxxxxxxxx
05.01.2006 06:40
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COBOL Programming on the iSeries/AS400 <cobol400-l@xxxxxxxxxxxx>


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Re: [COBOL400-L] Back with recursion in COBOL again!






Hello Roman,
                 sorry I checked the mail a bit late.Thanks a lot for 
taking 
the
                 pain of giving such an elaborate solution.
                 It really worked!
                 Now I realise ILE version of AS/400 Languages are feature 

rich enough
                 to be at par with any other open system languages like c 
or 
java.
                 Thanks for the Enlightenment!
Regards,
s.chand
>---------------------------------------------------------------------------------------------------
>------------------------------------------------------------------------------------------------------
>Here is better example for factorial, more likely to factorial's 
>pseudo(python)code

># factorial
>def factorial(n):
  if n == 0:
    result = 1
  else:
    result = n * factorial(n-1)
  return result

I coded it in COBOL as follows

       IDENTIFICATION DIVISION.
       PROGRAM-ID. FACTORIAL RECURSIVE.
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       SOURCE-COMPUTER. IBM-AS400.
       OBJECT-COMPUTER. IBM-AS400.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 RESULT       PIC 9(20).
       01 CALL-RESULT  PIC 9(20).
       01 N-MINUS-1    PIC 9(4).
       LINKAGE SECTION.
       01 N            PIC 9(4).

       PROCEDURE DIVISION USING BY VALUE N RETURNING RESULT.
           IF N = 0
              COMPUTE RESULT = 1
           ELSE
              COMPUTE N-MINUS-1 = N - 1
              CALL PROCEDURE 'FACTORIAL'
                   USING BY VALUE N-MINUS-1
                   RETURNING INTO CALL-RESULT
              COMPUTE  RESULT = N * CALL-RESULT
           END-IF.
           GOBACK.

note that I'm using calling by value n

the caller program is here

       IDENTIFICATION DIVISION.
       PROGRAM-ID. RECURTEST.
       ENVIRONMENT DIVISION.
       CONFIGURATION SECTION.
       SOURCE-COMPUTER. IBM-AS400.
       OBJECT-COMPUTER. IBM-AS400.
       SPECIAL-NAMES.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 N           PIC 9(4).
       01 RESULT      PIC 9(20).
       LINKAGE SECTION.
       PROCEDURE DIVISION.
           PERFORM VARYING N FROM 0 BY 1 UNTIL N = 21
             CALL PROCEDURE 'FACTORIAL'
                  USING BY VALUE N
                  RETURNING INTO RESULT
             DISPLAY N "! = " RESULT
           END-PERFORM.
       GOBACK.


now compile the FACTORIAL module, e.g.:
CRTCBLMOD MODULE(EBKPGMP/FACTORIAL) SRCFILE(RM/CBLJAVASRC)
SRCMBR(FACTORIAL)
DBGVIEW(*SOURCE)

create service program TMPPROC, e.g.:
CRTSRVPGM SRVPGM(EBKPGMP/TMPPROC) MODULE(EBKPGMP/FACTORIAL)
EXPORT(*ALL)

compile the RECURTEST module, e.g:
CRTCBLMOD MODULE(EBKPGMP/RECURTEST) SRCFILE(RM/CBLJAVASRC)
SRCMBR(RECURTEST)
DBGVIEW(*SOURCE)

and create the program RECURTEST with entry module RECURTEST linking it
with the saervice program TMPPROC, e.g:
CRTPGM PGM(EBKPGMP/RECURTEST)
ENTMOD(EBKPGMP/RECURTEST) BNDSRVPGM(EBKPGMP/TMPPROC)

Finally by calling that program CALL RECURTEST you will obtain these
results:

     0000! = 00000000000000000001
     0001! = 00000000000000000001
     0002! = 00000000000000000002
     0003! = 00000000000000000006
     0004! = 00000000000000000024
     0005! = 00000000000000000120
     0006! = 00000000000000000720
     0007! = 00000000000000005040
     0008! = 00000000000000040320
     0009! = 00000000000000362880
     0010! = 00000000000003628800
     0011! = 00000000000039916800
     0012! = 00000000000479001600
     0013! = 00000000006227020800
     0014! = 00000000087178291200
     0015! = 00000001307674368000
     0016! = 00000020922789888000
     0017! = 00000355687428096000
     0018! = 00006402373705728000
     0019! = 00121645100408832000
     0020! = 02432902008176640000


>So, from the above example it follows, that using modules and service 
>programs the recursion in ILE COBOL is possible in the  similar manner as 

>in the other languages.

>Roman

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