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COBOL General discussion FAQ


How to code control breaks? by slade
Posted: 9 Nov 02

This problem represents a major construct in business
programming, so the time you devote to this is well spent.

Input data is usually presented to a pgm in some sort sequence, e.g:


So you have a file level, an acct level, a product level and a date level. These levels are important because they are used to process the breaks in the program.

The general form is as follows:

       perform level n until level n-1 is finished

For the file described above the perform sequence would be:

       In the mainline you code:
          perform acct-lev until file-is-finished
       In the acct-lev you code:
          perform prod-lev until acct-is-finished
       In the prod-lev you code:
          perform date-lev until prod-is-finished
       In the date-lev you code:
          perform detl-lev until date-is-finished
       In the detl-lev you code:
          Aggregate all detl recs; aggregate all level
          totals; etc. Read next I/P det lrec.

OK now lets flesh this out. How do we determine when each level is finished? One way is to expand the function of the read routine to do this:

             move ws-ip-rec to ws-ip-prev
             read ip-file into ws-ip-rec
               at end set ip-eof to true
                  move high-values to ws-ip-rec  
              not at end add +1 to ws-ip-cnt
             perform 7010-set-breaks
             if curr-acct not = prev-acct
                set acct-is-finished to true
                set prod-is-finished to true
                set date-is-finished to true
             if curr-prod not = prev-prod
                set prod-is-finished to true
                set date-is-finished to true
             if curr-date not = prev-date
                set date-is-finished to true

Second question: We haven't read any data yet, how can we test if the levels are finished? We do a priming read outside of the loops, usually in the init or mainline section. After this read, if EOF is detected, an error msg is displayed and the pgm is usually exited because no input data has been provided.

How can the loops be executed if the "is-finished" switch has already been set? They can't. So, we reset the switch before executing each lower level:

           perform 7000-read-ip
           if ip-eof
              display error msg
              stop run
           perform 1000-acct-lev
             until file-is-finished
           perform 6900-print-rpt-end
           perform 9000-end-it
           stop run
           perform 6000-print-rpt-heads
           set reset-acct-sw to true
           perform 2000-prod-lev
             until acct-is-finished
           perform 6100-print-acct-tots
           zero tots, etc.
           set reset-prod-sw to true
           perform 3000-date-lev
             until prod-is-finished
           set reset-date-sw to true
           perform 4000-detl-lev
             until date-is-finished
           move ip data to rpt-line or whatever
           perform 7000-read-ip

Note that the form of each level except the detail level is:

Do pre-break stuff (print rpt heads, save data that won't be available after return from perform, etc.)

Reset the level switch.

Perform the next lower level.

Do post-break stuff (strike and/or zero or roll totals, write total recs, etc.)

At the detail level process the previous rec and read the next rec before exiting.

At entry to each level the record has already been read and is ready for processing.

Here's what a break switch would look like:

     01 ws-break-switches.
        05 ws-acct-sw                 pic x(001).
           88 acct-is-finished            value 'F'.
           88 reset-acct-sw               value 'R'.

This example has 2 break levels so your performs would look like:

           perform 8000-init
           perform 7000-read-ip
           if ip-eof
              display 'no data in i/p file'
              stop run
           perform 1000-process-codes
             until ip-eof
           set reset-code-sw to true
           perform 1100-process-detl
             until code-is-finished
           collect data, etc.
           perform 7000-read-ip

You have to ask: What do I do before the breaks; what do I do after. The answers to these questions may differ from project to project, but the basic concept: the cascading perform process is constant.

There are are other slightly more efficient ways of solving this problem but I tried to keep my version as "readable" as possible. If you do a keyword search on "construct" you will find them discussed in the thread started by "slade".    

This is one of the two major batch processing constructs in DP. The other is the file match. When I get some time I'll post something on this.

Let me know if this helps or if you have any questions.


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