The PROCEDURE
DIVISION
The procedure division is where the logic of
the program actually found. Here is where the various commands are written (see
Commands and logic section).
COBOL is a modular language, in that a program is usually
broken up into units described as paragraphs.
A D V E R T I S E M E N T
000900 PROCEDURE DIVISION.
000910 CONTROL-PARAGRAPH.
000920 PERFORM READ-DATA-FILE
000930 PERFORM CALULATE-PRICES
000940 PERFORM PRINT-PRICE-REPORT
000950 STOP RUN.
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The PERFORM statement is used to 'call' other paragraphs to
do each task. These paragraphs would appear in the same coding and are part of
the same program. In the above example, the program would consist of four
paragraphs: the CONTROL-PARAGRAPH and the three called from within it. All of
the paragraph names are user-defined. Even if a program only has one paragraph,
it must still have a name. The 'Hello
World' program has a paragraph name MAIN-PARAGRAPH. Regarding punctuation,
as a rule there should only be two full stops in any paragraph; one after the
paragraph name and the other at the end of the paragraph.
Sub-programs
A program may also refer to a different program, called a
sub-program. A sub-program is an entirely different program from the calling
program, with its own divisions etc... with the exception that it does not end
with STOP RUN (which would return you to the operating system), but with EXIT
PROGRAM. The sub-program is a module, rather than a subroutine which is what a
paragraph could be described as. The verb CALL is used to activate the
sub-program:
000800 DATA DIVISION.
000810 WORKING-STORAGE SECTION.
000820 01 W-DATE-IN PIC 9(6).
:
000850 LINKAGE SECTION.
000860 01 L-DATE-IN.
000870 03 DAY PIC 99.
000880 03 MONTH PIC 99.
000890 03 YEAR PIC 99.
:
000900 PROCEDURE DIVISION.
000910 CONTROL-PARAGRAPH.
000920 PERFORM READ-FILE
000930 CALL "VALIDATE-DATE" USING L-DATE-IN
:
001950 STOP RUN.
:
003000 IDENTIFICATION DIVISION.
003010 PROGRAM-ID. VALIDATE-DATE.
003020 ...........
: ............etc.....
003500 PRODECURE DIVISION USING L-DATE-IN.
:
004000 EXIT PROGRAM.
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In the above code, a sub-program is called, named
VALIDATE-DATE
In order to use data from the calling program in the
sub-program the calling program uses a section in the data division called the
LINKAGE SECTION. The item W-DATE-IN in the calling program occupies the same
memory address as the sub-program's item L-DATE-IN, so the number placed in
W-DATE-IN item using the VALUE clause is also in L-DATE-IN. Note: you cannot use
VALUE in the linkage section.
The procedure division of the sub-program requiring the
use of linkage section defined data must say so by: PROCEDURE DIVISION USING
...[linkage section items to be used] also refered to by the CALL ... USING. See
lines 000930 and 3500 above.
In the above example, what is being called
("VALIDATE-DATE") is a literal. This means that you could use an identifier
instead, allowing you a choice between sub-programs depending on what the
literal had been previously defined as. For example, if a record was of type "A"
then you may want to process that record using sub-program PROCESS-A-REC, but if
a type "B" record the use PROCESS-B-REC.
The logic might be as follows:
:
0003000 IF RECORD-TYPE = "A" THEN
0003010 MOVE "PROCESS-A-REC" TO SUB-PROG
0003020 ELSE MOVE "PROCESS-B-REC" TO SUB-PROG
0003030 CALL SUB-PROG USING L-REC-DATA
:
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Although I haven't described the various commands of the
procedure division (see Commands
and logic sections) the above code is fairly clear...if a marker called
RECORD-TYPE has been set as "A" then place (i.e. MOVE) the string
"PROCESS-A-REC" into the area of memory labelled as SUB-PROG (so now SUB-PROG
contains this string). Otherwise (i.e. ELSE) it is assumed that the only
other type there is can be "B" type and so "PROCESS-B-REC" is MOVEd into
SUB-PROG. Depending on what the item SUB-PROG contains the desired sub-program
will be called.
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