How to code control breaks?

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:


file
acct#1
product1
date1
date2
etc.
product2
date1
date3
date4
etc.
acct#2
product1
date3
etc.


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 detl rec

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:

7000-read-rtn.
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
end-read
perform 7010-set-breaks
.
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
end-if
if curr-prod not = prev-prod
set prod-is-finished to true
set date-is-finished to true
end-if
if curr-date not = prev-date
set date-is-finished to true
end-if


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:


0000-main-line.
perform 7000-read-ip
if ip-eof
display error msg
stop run
end-if
perform acct-lev until file-is-finished
perform 6900-print-rpt-end
perform 9000-end-it
stop run
.
acct-lev.
perform 6000-print-rpt-heads
set reset-acct-sw to true
perform prod-lev until acct-is-finished
perform 6100-print-acct-tots
zero tots, etc.
.
prod-lev.
set reset-prod-sw to true
perform date-lev until prod-is-finished
.
date-lev.
set reset-date-sw to true
perform detl-lev until date-is-finished
.
detl-lev.
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:

0000-mainline.
.
.
.
perform 8000-init
perform 7000-read-ip
if ip-eof
display 'no data in i/p file'
stop run
end-if
perform 1000-process-codes until ip-eof
.
.
.
1000-process-codes.
set reset-code-sw to true
perform 1100-process-detl until
code-is-finished
.
1100-process-detl.
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 some-
thing on this.

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

Jack