1

Structured COBOL Programming

Nancy Stern Hofstra University

Robert A. Stern Nassau Community College

James P. Ley University of Wisconsin-Stout

John Wiley & Sons, Inc.

PowerPoint Winifred J. Rex Presentation Bowling Green State University

10th edition

2

An Introduction to Structured Program Design in COBOL

Chapter 1

Please note that the original slides will be modified in a numberof places by your professor.

These changes are for pedagogical reasons.

3

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

4

Chapter Contents

Computer Programming: An Overview Applications Program Development Process Nature of COBOL History of COBOL and the ANS Versions Techniques for Improving Program Design Sample Programs Entering and Running a COBOL Program on

Your Computer

5

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

Oftentimes called System Software Applications programs - perform tasks required

by users Often called Applications Software Us.

6

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

Program to generate a Payroll Program to generate and print an Inventory

Listing

7

Application Programs - Customized

Written for specific users like doctors, car dealerships

Necessary if user has special requirements

8

Applications Package – General Usage

Written for general user who needs program to perform standard tasks

Standard tasks include budgeting, scheduling payroll, etc.

Cheaper, easier than writing customized program

9

Program Languages

Machine language Only language computer understands All programs executed on computer must be

in machine language Machine language programs difficult to write Written in binary, such as:

0001101001010100 (actual instruction) 010110101000000011000100 (actual

instruction in binary)

10

Assembler Languages

Level ‘higher’ than Machine Language. Use mnemonic codes rather than pure binary

digits, such as:L R5,X

AR R5,R4

ST R5,SUM

Each of these instructions translates (normally one-to-one) into a machine language statement (that is, binary…)

11

Program Languages

Symbolic language (like COBOL) Called Higher-Level Languages English-like languages used to write

programs Easier than writing programs in machine

language or assembly languages. Must be translated or compiled into machine

language to run on computer

12

Program Development Process

1. Determine Program Specifications – the “Whats”

2. Design Program Using Program Planning Tools – the “Hows.”

3. Code and Enter Program (using some editor)

4. Compile Program Implementation

5. Test Program

6. Document Program

13

1. Program Specifications• Systems analysts, users and programmers develop

specifications• Specifications include:

• Description of input and output data• Description of what the program must do to the input to

convert it to the output - that is, WHAT the program is to do.

• They may provide formulas, constraints on data, conditions, etc. etc. BUT (again, not How the developers accomplish this!)

• In a perfect world, Systems Analysts specify the ‘requirements’ needed. (doesn’t always work this way.)

14

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) Please note that exactly WHO does this may vary

depending on the expertise of the systems analysts, developers, etc. But these are part of the Specifications.

15

1. Program Specifications

Printer spacing charts describe Spacing of outputs (see pp 6-7)

hard copy reports screen layouts, etc.

Layout of printed output Heading, detail, total lines Error messages and locations…

16

2. Design the Program

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

Once specifications are captured (discuss!), design takes place.

Two real kinds of design: Architectural design (high level, parts;

components, blocks of functionality; relationships among these blocks, and

Detail design – the logic inside each block, part, component, etc.

17

2. Design the Program

Different tools may be used to capture the preliminary (architectural) design as well as the detail (logic; algorithms) design.

Architectural Design: For many traditional systems, we may use Data Flow

Diagrams; Structure Charts, System Flow Charts, and similar technologies

For Detail design: Most practitioners use flowcharts, pseudocode, HIPO,

or other techniques to capture the module logic.

18

Architectural design: Book suggests Hierarchy charts show relationships among sections of program. We will use these and call them Structure

Charts. Book cites for Detail Design:

Flowcharts use block diagrams to represent logic – a graphical model, and

Pseudo-code uses English-like statements This one is preferred but some hang on to the

flowchart. In some cases, it ‘is’ clearer, though.

19

3. Code and Enter Program

Programmer writes and enters program into computer

Program written in symbolic language (like COBOL)

Called source program

20

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 (See p. 8 for System Flow Chart. Know this.)

21

5. Test Program

Test or debug program to ensure it contains no errors

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

22

Compile-Time Errors

Errors detected by compiler during translation from COBOL to machine language

Detects violations of programming rules Misspelled reserved words Missing punctuation Errors in use of the programming language

Also called syntax errors

23

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

24

Debugging Techniques

Desk checking always do this. Can be costly to omit.

Correcting syntax errors Correct syntax errors and resubmit

Program walkthroughs Sometimes done in teams; good approach Can be done prior to submitting for compilation.

Executing the program Just because a program runs to EOJ, does NOT

mean that program was successful!!

25

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 In some circles called: program maintenance

manual, operators manual, users manual, etc…

26

Nature of COBOL

Business-oriented language Great for business data processing Large volumes of data Great for data manipulation

No language is better for transaction processing or data manipulation than COBOL

Has other major deficiencies, but not these.

Standard language English-like language

Multiply hours-worked by rate giving salary Relatively easy to understand

27

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

28

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

29

Current and Future Standards

1985 currently the most widely used Sometimes called COBOL 2.

2002+ is next standard Approval expected in 2002 Information on 2002+ COBOL standard at

http://www.ansi.org

30

Future of COBOL

Likely to remain important language Unlike academic environment, most programs

are developed to be used for many years to realize a ROI. This implies the need to maintenance as requirements change and errors are discovered.

Older COBOL programs need to be updated Still used by many for new program

development

31

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

32

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

33

Year 2000 Problem (Y2K)

Many calculations with dates incorrect starting in 2000

To find your age if you were born in 1970Subtract 70 from 95 (95 - 70 = 25)

Calculation incorrect for year 2000 and beyond

00 - 70 = -70 when age should be 30

34

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 correct

1995 - 1970 = 25

2000 - 1970 = 30

35

Improving Program Design

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

Structured Programming

Top-Down Programming

36

Structured Programming

Eliminates use of GO TO statements Allowed skipping to different sections of program

without returning to starting point Advocated the use of simple program constructs:

sequence selection iteration plus two extensions (later)

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

37

Structured Programming

Program divided into paragraphs Main paragraph or module controls logic flow using

PERFORM statements Sometime called a ‘driver’ module…

Main module "performs" other modules when instructions in that module required Control transferred to a different paragraph and,

upon completion of the instructions in that paragraph, control returns to the main paragraph.

Each module can be written and tested independently of others

38

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

39

Top-Down Programming

For COBOL program Code main modules or routines first Code intermediate modules next Details deferred to minor modules and coded

last We will use this technique a lot later on. We

may refer to this technique as ‘drivers’ and ‘stubs.’ This is an outstanding approach to developing

larger programs…