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COBOL for the 21st Century

Nancy Stern Hofstra University

Robert A. Stern Nassau Community College

James P. Ley University of Wisconsin-Stout (Emeritus)

John Wiley & Sons, Inc.11th edition

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An Introduction to Structured Program Design in COBOL

Chapter 1

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Chapter Objectives

To familiarize you with

• Why COBOL is a popular business-oriented language.

• Programming practices and techniques• History of COBOL • Use of the current ANSI standard

versions of COBOL• Four divisions of a COBOL program

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Chapter Contents

• Computer Programming: An Overview• Applications Program Development

Process• Nature of COBOL• History of COBOL and the ANS

Versions

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Chapter Contents

• Techniques for Improving Program Design

• Sample Programs• Entering and Running a COBOL

Program on Your Computer

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Computer Program

• A set of instructions that enables computer to process data

• Also called software

• Two types of computer programs– Operating system programs - control

overall operations of computer– Applications programs - perform tasks

required by users

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Applications Programs

• Written by applications programmer• May provide quick solution to one-time

problem– Displaying average grade for set of exam

scores

• Or may be run on regularly scheduled basis– Program to print student transcripts each

semester

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Customized Application Programs

• Written for specific users like doctors, car dealerships

• Necessary if user has special requirements

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Applications Package

• Written for general user who needs program to perform standard tasks

• Standard tasks include budgeting, scheduling payroll, etc.

• Cheaper, easier than writing customized program

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Program Languages

Machine language• Only language computer understands• All programs executed on computer

must be in machine language• Machine language programs difficult to

write

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Program Languages

Symbolic language (like COBOL)• English-like languages used to write

programs• Easier than writing programs in machine

language• Must be translated or compiled into

machine language to run on computer

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Program Development Process

1. Determine Program Specifications

2. Design Program Using Program Planning Tools

3. Code and Enter Program

4. Compile Program

5. Test Program

6. Document Program

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1. Program Specifications

• Systems analysts, users and programmers develop specifications

• Specifications include:• Description of input and output data• Step-by-step processing required to

convert input to output

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1. Program Specifications

Record layout forms describe format of input and output data

• Data names of each data item in record

• Location of each data item in record

• Size of each data item

• Number of decimal positions (for numeric data items)

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1. Program Specifications

Printer spacing charts describe

• Spacing

• Layout of printed output

• Heading, detail, total lines

• Error messages

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2. Design the Program

Program planning tools used to map out structure and logic of program

• Flowcharts use block diagrams to represent logic

• Pseudocode uses English-like statements

• Hierarchy charts show relationships among sections of program

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3. Code and Enter Program

• Programmer writes and enters program into computer

• Program written in symbolic language (like COBOL)

• Called source program

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Source program in symbolic language

Object program in machine language

Translated by compiler

4. Compile Source Program

Compiler is program that

• Checks source program for rule violations

• Translates source program into object program

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5. Test Program

• Test or debug program to ensure it contains no errors

• Check for two types of errors– Compile-Time Errors– Execution Errors

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Compile-Time Errors

• Errors detected by compiler during translation from COBOL to machine language

• Detects violations of programming rules– Misspelled reserved words– Missing punctuation

• Also called syntax errors

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Execution Errors

• Detected when program is run

• Logic error causes incorrect output– Sequence of instructions incorrect– Wrong instruction coded

• Run-time error if computer cannot execute instruction– Attempt to divide by zero– Attempt to read a file that cannot be found

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Debugging Techniques

• Desk checking

• Correcting syntax errors

• Program walkthroughs

• Executing the program

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6. Document the Program

• Documentation - formal set of procedures and instructions to specify how to use program

• Written for– Those working with output– Computer operators who run program– Maintenance programmers who make

modifications to program

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Nature of COBOL

• Business-oriented language

• Standard language

• English-like language

• Relatively easy to understand

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History of COBOL

• Developed in 1959 as standard language to meet needs of business

• Committee to develop language convened by Department of Defense

• Included representatives from academia, business, computer manufacturers

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Standard Versions of COBOL• 1960s

• 1968

• 1974

• 1985

wide variations in COBOL compilers

first COBOL standard set by American National Standards Institute (ANSI)

second ANSI standard to make COBOL more efficient, standardized

this ANSI standard incorporated structured programming techniques

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Current and Future Standards

• 1985 currently the most widely used

• 2008 is next standard – Approval expected in 2008 or so– Information on 2008 COBOL standard at

http://www.ansi.org

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Future of COBOL

Likely to remain important language

• Older COBOL programs need to be updated

• Still used by many for new program development

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Use of COBOL

• About 200 billion lines of COBOL source code in use

• 5 billion new lines added each year

• Used by 42.7% of application programmers in medium to large U.S. companies

• $200 million in expected revenues for 2001

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Year 2000 Problem (Y2K)

• Year stored as two digits in older programs to save space

• 19 assumed as valid prefix for all years– 95 represented year 1995

• Invalid as prefix for years 2000 and beyond– 00 could mean 1900 or 2000

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Year 2000 Problem (Y2K)

Many calculations with dates incorrect starting in 2000

• To find your age if you were born in 1970

Subtract 70 from 95 (95 - 70 = 25)

• Calculation incorrect for year 2000 and beyond

00 - 70 = -70 when age should be 30

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Year 2000 Problem (Y2K)

To correct problem

• Billions of lines of code, many written in COBOL needed to be examined

• Code changed to use four digits for year

• Age, other calculations now correct1995 - 1970 = 25

2000 - 1970 = 30

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Year 2000 Problem (Y2K)

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Year 2000 Problem (Y2K)

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Improving Program Design

Two techniques used to develop programs that are easier to understand, test, debug and modify

• Structured Programming

• Top-Down Programming

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Structured Programming

• Eliminates use of GO TO statements – Allowed skipping to different sections of

program without returning to starting point

• Program logic easier to follow with "GO-TO-less" programming

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Structured Programming

Program divided into paragraphs

• Main paragraph or module controls logic flow using PERFORM statements

• Main module "performs" other modules when instructions in that module required

• Each module can be written and tested independently of others

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Top-Down Programming

• Another technique to make programs easier to understand, test, debug and modify

• Develop program like term paper– Develop outline first– Add details for each of main steps– Add further refinement for more complex

steps

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Top-Down Programming

For COBOL program

• Code main modules or routines first

• Code intermediate modules next

• Details deferred to minor modules and coded last

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Interactive vs Batch Programs

• Cobol suited for developing both types of programs

Interactive programs

• Accept input data from keyboard

• Input data processed immediately

• Output (results) displayed on screen immediately

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Interactive vs Batch Programs

Batch programs

• Process large volumes of input at periodic intervals

• Input data read in from files

• Output written to files

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Overview of the Four Divisions

• Every COBOL program contains up to four separate divisions in the following order:

IDENTIFICATION DIVISION

ENVIRONMENT DIVISION

DATA DIVISION

PROCEDURE DIVISION

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Overview of the Four Divisions

• IDENTIFICATION DIVISION– Identifies program to operating system– Provides documentation about program

• ENVIRONMENT DIVISION– Defines file-names– Describes devices used to store them– Not included in fully interactive programs

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Overview of the Four Divisions

• DATA DIVISION– Describes input and output format of data

in files– Defines any constants and work areas

• PROCEDURE DIVISION– Contains instructions to read input, process

it and create output

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Sample Interactive Program

• Purpose– to compute employee WAGES

• Input from keyboard– HOURS and RATE

• Processing– compute WAGES as HOURS x RATE

• Output displayed on screen– WAGES

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Sample Interactive Program

• IDENTIFICATION DIVISION– One required entry, PROGRAM-ID– Names the program

• DATA DIVISION– Describes and defines storage for all data – Data defined in WORKING-STORAGE

SECTION for interactive program

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Data Defined in Sample Program

• Keyed input fields (HOURS, RATE)• Output fields (WAGES)• Other fields used for processing

(MORE-DATA)

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PICTURE Clause

• 01 level begins definition of each field• PICTURE or PIC clause describes

– Type of data• Numeric (PIC 9)• Nonnumeric (PIC X)

– Size of field - determined by number of 9’s or X’s

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PICTURE Clauses

• RATE with PIC 99V99 includes V to show assumed decimal point position

• User enters data with decimal point– Program uses V to align data

• WAGES includes actual decimal point – Shown when value displayed on screen

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Giving Field Initial Value

• MORE-DATA with PIC XXX is nonnumeric field

• Assigned initial contents of YES by use of VALUE clause

• Value must be in quotation marks since MORE-DATA is nonnumeric field

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PROCEDURE DIVISION

• Set of instructions to be executed by program

• Organization of instructions planned before coding begins

• Pseudocode, an English-like description of program instructions, used for planning

• Describes program logic and order in which instructions will be executed

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PROCEDURE DIVISION

• PROCEDURE DIVISION includes one paragraph 100-MAIN

• List of instructions that follow make up paragraph

• Period follows last statement in paragraph (STOP RUN.)

• Main processing controlled by PERFORM … END-PERFORM loop

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PERFORM … END-PERFORM

• Repeats set of instructions as long as user enters YES in response to prompt

"IS THERE MORE DATA (YES/NO)?"

• MORE-DATA initially contains YES so instructions in loop executed first time

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PERFORM … END-PERFORM

• When user enters NO as response– MORE-DATA set to "NO" and loop ends

• After loop, STOP RUN is executed, ending program

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PERFORM … END-PERFORM

Statements in loop executed in order they are listed

• DISPLAY displays value in quotes or value of field on screen

• ACCEPT stores value user enters from keyboard in field

• MULTIPLY performs calculation to find WAGES

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Sample Batch Program

• In batch mode, data comes from input file instead of keyboard

• Data for each employee stored in a record in file on disk

• Employee name, hours and rate data called fields

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Sample Batch Program

• Calculated results (Wages) stored in file instead of displayed on screen

• For each input record– Record created and stored in output file– Includes employee name, hours, rate and

computed wages – File intended for printing so spacing added

between fields for readability

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COBOL Divisions

• All four divisions included for batch programs

• IDENTIFICATION DIVISION first with required PROGRAM-ID paragraph

• ENVIRONMENT DIVISION– INPUT-OUTPUT SECTION assigns input

and output files to specific devices

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DATA DIVISION

• FILE SECTION describes format of input and output files

• Fields in records described using PICTURE clause

• Decimal point not stored in input records– Use V for implied decimal for alignment

• Use actual decimal point for fields in output record so it is printed

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PROCEDURE DIVISION

• Contains instructions to be executed by computer

• Instructions executed in order they appear

• Includes two paragraphs with period at end of each

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100-MAIN-MODULE

• OPENs files to be used by program

• Repeatedly READs in records (PERFORM … END-PERFORM) until there are no more

• Calls second paragraph 200-WAGE-ROUTINE to process each record

• CLOSEs files after all records read

• Ends program (STOP RUN)

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READ Statement

• Reads one record into program storage area

• Record must be in storage to use it

• Takes one of two actions depending on whether record was read

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READ Statement

• PERFORM instruction after NOT AT END executed when record read– Statements in paragraph 200-WAGE-

ROUTINE executed to process record

• If no more records to be read, MOVE instruction after AT END executed– 'NO ' moved to ARE-THERE-MORE-

RECORDS, ends loop

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200-WAGE-ROUTINE

• First MOVE initializes PRINT-REC to blanks

• Then MOVEs name, hours, wages to output fields

• Calculates WAGES with MULTIPLY statement, MOVES it to output field

• WRITEs data in employee output record to print file

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Entering & Running a Program

To type in and run a COBOL program on your computer system, you need to know how to:

• Log on and off of the computer

• Name COBOL files on the computer

• Use a text editor to key in, modify and save files

• Compile a COBOL source program to translate it into machine language

• Link or load the object program

• Run the object program

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Chapter Summary

• The Nature of COBOL– English-like language – Used widely for business programming– With new standard coming out soon, it is

likely to remain important language

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Chapter Summary

• Use planning tools and good design techniques to improve program design

• Document programs well

• Carefully test and debug programs

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Chapter Summary

COBOL programs divided into four divisions

• IDENTIFICATION DIVISION identifies program to operating system

• ENVIRONMENT DIVISION required for batch programs that operate on files

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Chapter Summary

• DATA DIVISION defines formats for all input, output and work areas needed– FILE SECTION required for batch

programs that operate on files– WORKING-STORAGE SECTION for work

fields or fields used in interactive programs

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Chapter Summary

• PROCEDURE DIVISION– Contains instructions to process input and

produce output– Divided into paragraphs or modules

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Copyright © 2003 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in Section 117 of the 1976 United States Copyright Act without the express written permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages, caused by the use of these programs or from the use of the information contained herein.

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An Introduction to Structured Program Design in COBOL

Chapter 1