COBOL Basics

Lets first understand the basic structure of a COBOL program, how it is divided and the reason.

Divisions Of Cobol Program

A COBOL program has 4 divisions and they are 


IDENTIFICATION DIVISION
ENVIRONMENT DIVISION
DATA DIVISION
PROCEDURE DIVISION

Identification Division

This is the first and the only mandatory division of a COBOL program. It is used to supply information regarding the identity of the program to the compiler. This is how the division is coded in MARGIN A which starts at 8th byte. Think of this division as a one word documentation of a program.


IDENTIFICATION DIVISION.
Program-ID. HelloWorld.
Author. ProgrammersPub.
Installation. ProgrammersPub.
Date-Written. 18/03/2021.
Date-Compiled. 18/03/2021.
Name Required
Program-ID Mandatory
Author Optional
Installation Optional
Date-Written Optional
Date-Compiled Optional

Environment Division

Environment Division describes the computing environment to the compiler in which the program will run. It consists of two sections,

CONFIGURATION SECTION and INPUT-OUTPUT SECTION. Each section has its own paragraphs as seen below.


ENVIRONMENT DIVISION.
CONFIGURATION SECTION.
	SOURCE-COMPUTER. [Value].
	OBJECT-COMPUTER. [Value].
	SPECIAL-NAMES. [Value].
INPUT-OUTPUT SECTION.
	FILE-CONTROL. [Value].
	I-O CONTROL. [Value].
Name Description
SOURCE-COMPUTER System where the program is compiled
OBJECT-COMPUTER System where the program is executed
SPECIAL-NAMES Special items such as the currency sign and symbolic characters
FILE-CONTROL Provides information about datasets that are used in the program
I-O CONTROL Specifies information needed for efficient transmission of data between the external data set and the COBOL program.

The FILE-CONTROL is used to link the dataset between JCL and COBOL program. Here is an example


       IDENTIFICATION    DIVISION.                                      00010000
       PROGRAM-ID. REPORT1.                                             00020000
      *                                                                 00030000
       ENVIRONMENT       DIVISION.                                      00040000
       INPUT-OUTPUT      SECTION.                                       00050000
       FILE-CONTROL.                                                    00060000
      *                                                                 00070000
            SELECT EXTRACT ASSIGN TO DD1                                00080000
            ORGANIZATION IS SEQUENTIAL                                  00090000
            ACCESS MODE IS SEQUENTIAL                                   00100000
            FILE STATUS IS WF-EXTRACT.                                  00110000
      *                                                                 00120000
            SELECT PAY-REPORT ASSIGN TO DD2                             00130000
            ORGANIZATION IS SEQUENTIAL                                  00140000
            ACCESS MODE IS SEQUENTIAL                                   00150000
            FILE STATUS IS WF-PAY-REPORT.                               00160000
      *                                                                 00170000
Name Description
SELECT The SELECT clause chooses a file in the COBOL program to be associated with an external data set
ASSIGN The ASSIGN clause associates the program’s name for the file with the external name for the actual data file. You
can define the external name with a DD statement
ORGANIZATION The ORGANIZATION clause describes the file’s organization. For QSAM files, the ORGANIZATION clause is optional
ACCESS MODE The ACCESS MODE clause defines the manner in which the records are made available for processing: sequential,
random, or dynamic. For QSAM and line-sequential files, the ACCESS MODE clause is optional. These files always
have sequential organization.
FILE STATUS It is a variable where the status of the file is saved.

For VSAM files, you might have additional statements in the FILE-CONTROL paragraph depending on the type of VSAM file you use.

Data Division

Data Division provides the descriptions of the data to be processed by the program used in input and output operations.


DATA DIVISION.
FILE-SECTION.
...
WORKING-STORAGE SECTION.
...
LINKAGE SECTION.
...
REPORT SECTION.
LOCAL STORAGE SECTION.
SCREEN SECTION.

Example:


       IDENTIFICATION    DIVISION.                                      00010000
       PROGRAM-ID. REPORT1.                                             00020000
      *                                                                 00030000
       ENVIRONMENT       DIVISION.                                      00040000
       INPUT-OUTPUT      SECTION.                                       00050000
       FILE-CONTROL.                                                    00060000
      *                                                                 00070000
            SELECT EXTRACT ASSIGN TO DD1                                00080000
            ORGANIZATION IS SEQUENTIAL                                  00090000
            ACCESS MODE IS SEQUENTIAL                                   00100000
            FILE STATUS IS WF-EXTRACT.                                  00110000
      *                                                                 00120000
            SELECT PAY-REPORT ASSIGN TO DD2                             00130000
            ORGANIZATION IS SEQUENTIAL                                  00140000
            ACCESS MODE IS SEQUENTIAL                                   00150000
            FILE STATUS IS WF-PAY-REPORT.                               00160000
      *                                                                 00170000
       DATA            DIVISION.                                        00180002
       FILE            SECTION.                                         00190002
      *                                                                 00191001
      *---->INPUT FILE                                                  00192001
      *                                                                 00193001
       FD EXTRACT.                                                      00200001
          COPY PAYROLL.                                                 00210001
      *                                                                 00220001
      *----> OUTPUT FILE                                                00230001
      *                                                                 00240001
       FD PAY-REPORT.                                                   00250001
          01 REPORT-REC              PIC X(80).                         00260001
      *                                                                 00270001
       WORKING-STORAGE SECTION.                                         00280002
      *                                                                 00290002
       01 WS-DATE-RNAME.                                                00300003
          05 FILLER                  PIC X(02).                         00310002
          05 FILLER                  PIC X(15) VALUE 'PAYROLL REPORT'.  00320002
          05 FILLER                  PIC X(53).                         00330002
          05 WS-SYS-DATE             PIC X(08).                         00340002
          05 FILLER                  PIC X(02).                         00350002
      *                                                                 00360002
Name Description
FILE-SECTION The file section defines the structure of data files
WORKING-STORAGE SECTION The working-storage section describes data records that are not part of data files but are developed and processed by a program. Think of it as a temporary variable and file structure.
LINKAGE SECTION The linkage section describes data made available from another program example when calling sub-programs.
LOCAL STORAGE SECTION Same as working storage, but local storage is specific to program invocation.  On each invocation, data items defined in the local-storage section are reallocated. Each data item that has a VALUE clause is initialized to the value specified in that clause.
SCREEN SECTION Used as inline cics screen.

Procedure Division

All the data described in the DATA DIVISION are processed here. This division has the custom defined business logic of the program. Example,


IDENTIFICATION DIVISION.          
PROGRAM-ID. HELLO1.               
ENVIRONMENT DIVISION.             
DATA DIVISION.                    
PROCEDURE DIVISION.               
    0000-INPUT-PARA.                  
    DISPLAY "HELLO WORLD".        
    STOP RUN

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