Introduction Cobol

Structured COBOL Programming, Stern & Stern, 9th edition

Chapter 1INTRODUCTION TO

STRUCTURED PROGRAM DESIGN IN COBOL


CHAPTER 1 OBJECTIVESCHAPTER 1 OBJECTIVES To familiarize you with:

1. The reasons for COBOL’s popularity as a business-oriented language.2. Some general programming practices and techniques.3. A history of COBOL’s evolution and its current ANS version.4. An overview of how a COBOL program is structure.


Types of Computer ProgramsTypes of Computer Programs

A program is a set of instructions that enable a computer to process data.

Software is the term used to describe all types of programs.

An application program converts input data to output information.


IPO Chart / System Flowchart

IPO Chart / System Flowchart

Identifies the inputs and outputs of the program. Basic IPO model.

EMPLOYEE FILE

PRINT PAYROL DATA PAYROLL

REPORT


Two types of computer programs:Two types of computer programs:

1. Operating Systems Programs Control the overall operations of the computer

2. Applications ProgramsWritten by Programmers or Software DevelopersPrograms that perform tasks required by usersA set of programs that fulfill a business requirement is an Information System


Applications ProgramsApplications Programs

Interactive vs. Batch Processing Interactive applications typically accept input data

from a PC, workstation, or terminal. Batch Processing applications process large

volumes of input at periodic intervals.DailyWeeklyMonthly etc.


Applications Programs Applications Programs

Applications programs that are written for a specific user are called customized programs.

Programs that are relatively standard are application packages that might be purchased.

Off The Shelf (OTS) may be less costly depending on the amount of customization needed


All programs executed by the computer must be in machine language – the only language a computer understands

Binary 10110101 Must know memory address of variables etc.

Machine Language ProgramsMachine Language Programs


Symbolic ProgramsSymbolic Programs Symbolic Programs use English-like or

symbolic instructions.These programs must be translated or compiled into machine language.– Symbols (Variable/Data names) represent memory

addressesCOBOL is a symbolic programming language used for commercial applications.As is C++, Visual Basic etc.

A compiler coverts symbolic language into machine code


Program Development ProcessProgram Development Process

1. Determine Program Specifications2. Design Program Using Program Planning Tools3. Code and Enter Program4. Compile Program5. Test Program6. Document Program


PROGRAM DEVELOPMENT PROCESSPROGRAM DEVELOPMENT PROCESS

1. Determine Program SpecificationsProgram Specifications consist of the following:–Record layout forms to describe the input and

output (pg 6)–Printer spacing charts for printed output (pg 7)–Any special rules for processing


I/O SpecificationsI/O SpecificationsThe I/O specifications establish record names, field names, data sizes and types to be used in your program. For auxiliary storage specifications can take the form of an 01 level print out or a simply chart as follows.

Used in developing the Data Division.

Payroll-Record

Type Size

Name Alphanumeric 30

Address Alphanumeric 23

Pay-Rate Numeric 5.2 or 7 with 2 decimals

Etc.



2. Design the Program Using Program Planning Tools using Common Tools:

Hierarchy Charts– Charts showing relationships among sections in a programFlowcharts– A block diagram providing a pictorial representation of the

logic to be used in a programPseudocode– English-like expressions to depict the logic of the program


HIERARCHY CHARTHIERARCHY CHART

3 0 0-G E T -D A T E 9 0 0-P R IN T -H E A DE RS

2 00 - IN IT IA LIZE

3 1 0-F IND -RA T E

9 0 0-P R IN T -H E A DE RS

3 2 0-P R INT -D E T A ILS

2 1 0 -P R O CE S S -R E C O R DS

1 0 0-C A L C UL A T E -V E HIC LE -RE G IS T R A T IO N -FE E S

The first phase of problem solving is to use a top down design. Begin with a very general problem statement and break it down into smaller and smaller pieces until you know you have pieces you can solve.

The hierarchy chart establishes the Paragraph names you will use in pseudo code and in your program’s Procedure Division. It outlines a very general program flow and shows the relationship between modules/paragraphs.

Answers the question WHAT needs to be done?

REMEMBERREMEMBER

The sooner you start coding the longer it will take you to complete the project!!!!!


To Reduce Cost of Fixing ErrorsTo Reduce Cost of Fixing Errors

Phase in which error is detected

Relative cost of repair

Requirements 0.1 – 0.2

Design 0.5

Coding 1 2X

Program testing 2 4X

Acceptance test 5 10X

Maintenance 20 40X



3. Code and Enter the ProgramThe programmer writes and then keys or enters the source program into the computer system using a keyboard.

4. Compile the ProgramThe COBOL compiler checks the source code to insure there are no rule violations. A syntax error is a type of error that is found if a programming rule is violated.

Source program in symbolic language

Object program in machine language

Translated by compiler


PROGRAM DEVELOPMENT PROCESSPROGRAM DEVELOPMENT PROCESS5. Test the Program

Programs are tested or debugged to ensure they have no errors.Runtime errors–A logic error produces incorrect results–An Operating System violation –results in program

termination6. Document the Program

Procedure manuals for users and computer operators, called documentation, is prepared for use by the operating staff for regular production.


PROGRAM DEVELOPMENT PROCESS PROGRAM DEVELOPMENT PROCESS

Remember, coding is undertaken only after the program requirements have been fully specified and the logic has been carefully planned.


DEBUGGING TECHNIQUESDEBUGGING TECHNIQUES

Desk Checking Reviewing the program before and after keying

Correcting Syntax ErrorsUsing the printed source list of the diagnostic messages to find and correct the errors


DEBUGGING TECHNIQUES DEBUGGING TECHNIQUES Program Walkthroughs

Manually stepping through the program with test data.

Detecting Logic Errors by Executing the Program

Often the most difficult part of debugging. The preparation of test data is an extremely critical aspect of debugging.


THE NATURE OF COBOLTHE NATURE OF COBOL

COBOL is a Business-Oriented LanguageCOBOL, is one of the most widespread commercial applications languages in use today.

COBOL is an abbreviation for COmmon Business Oriented Language,

COBOL is a Standard LanguageCOBOL is a common programming language available on most computers.


THE NATURE OF COBOLTHE NATURE OF COBOLCOBOL is an English-like Language

All instructions can be coded using English words.The rules conform to many rules for writing in English

COBOL is a User-Friendly LanguageBecause users are able to understand the English-like instructions it is considered a user-friendly language.


WHEN IT BEGANWHEN IT BEGAN

Developed in 1959 by the CODASYL Committee.A committee consisting of representatives members from academia, user groups, and computer manufacturers.

Developed as a standard business-oriented language for which all major manufacturers would provide compilers.

ANS established the first standards version in 1968. COBOL ’85 the current standard http://www.ansi.org 2002+ Standard


THE FUTURE OF COBOLTHE FUTURE OF COBOL COBOL is likely to remain an important

language in the years ahead for two reasons:1. Older, mainframe-based “legacy” systems will

need to be maintained by maintenance programmers who know COBOL.

2. COBOL is still being used by many organizations for new application development.


Use of COBOLUse 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


Interactive vs Batch ProgramsInteractive 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


Interactive vs Batch ProgramsInteractive vs Batch Programs

Batch programs Process large volumes of input at periodic

intervals Input data read in from files Output written to files


TECHNIQUES FOR IMPROVING PROGRAM DESIGN

TECHNIQUES FOR IMPROVING PROGRAM DESIGN


Improving Program DesignImproving Program DesignTwo techniques used to develop programs that are

easier to understand, test, debug and modify

Structured Programming

Top-Down Programming


Structured ProgrammingStructured 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


Structured ProgrammingStructured 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


Top-Down ProgrammingTop-Down Programming

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

Develop program like term paperDevelop outline firstAdd details for each of main stepsAdd further refinement for more complex steps


Top-Down ProgrammingTop-Down Programming

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

last


Program SpecificationsProgram Specifications

System Flowchart Input/Output Specifications Hierarchy Chart Psuedo code Narrative – as comments in program


Attendance Report

INPUT PROCESSING OUTPUT

System Flowchart

Student-File

PRINT STUDENT

ATTENDANCE


START

OPEN FILES

READFIRST

RECORD

WRITEHEADINGS

END OFFILE

REACHED?

PROCESSRECORDS

CLOSEFILES

STOP

PROCESSRECORDS

ENGINEERINGMAJOR ANDMORE THAN110 CREDITS

WRITESTUDENT

NAME

READNEXT

RECORD

STOP

Program Flow Chart1

2

3

4

5

6

7

8

FALSE TRUE

9

10

11

12

(a) Overall Flowchart (b) Detail of PROCESS-RECORDS


Initialization

Processing

Termination

Open files

Read first record

Write heading

DO while data remains

IF engineering major with more than 110 creditsWrite student’s name

ENDIF

ENDDO

Close files

Stop

Pseudo Code


Hierarchy of DataHierarchy of Data Bit - binary 0 or 1 Byte / Character - 8 bits Field - a basic fact about some entity

Customer - Current-BalanceInventory - Selling-Price

Record - a collection of related facts File - a collection of related records Database - an organization’s set of files


Figure 1.1 Fields, Records, and Files

Fields(Facts)

Records(Set of Fields)

Name: John AdamsCredits: 90Major: Political Science

Name: Amelia EarhartCredits: 120Major: Aviation

Name: Orville WrightCredits: 115Major: Engineering

Name: Georgia O’KeeffeCredits: 125Major: Art

Jphn Adams 90 Political Science

Amelia Earhart 120 Aviation

Orville Wright 115 Engineering

Georgia O’Keeffe 125 Art


Programming StructuresProgramming Structures

Sequence Selection Iteration/Repetition


Structured Programming Using Modular Design for Coding Paragraphs


The most important technique for improving the design of a program in any language is called structured programming.

Structured Programming is a technique using logical control constructs that make programs easier to read, debug, and modify if changes are required.


Modular ProgrammingModular Programming

Each module/paragraph must meet the following characteristic

COMPLETENESS – taken together the modules completely satisfy the program specificationsCOHESIVE – a paragraph must perform one and only one taskCOUPLING – paragraphs are loosely coupled – that is a paragraph does not depend on other paragraphs




Structured programming is often called GO-TO-less programming since programmatic branches do not use GO TO statements.

In COBOL this means writing programs using PERFORM statements




The typical structured program is divided into paragraphs or modules, where a main module calls in other modules as needed.

Each block on the hierarchy chart represents a paragraphEach module can be tested independently.– Paragraph, routine, module are used interchangeably


The Top-Down Approach for Coding ModulesThe Top-Down Approach for Coding Modules

Proper design is best achieved by developing major modules before minor ones.

Main routines are coded first and are followed by intermediate routines and then minor ones.

Coding using the top-down manner gives the primary attention to the origination of the program.

Details are deferred or saved for minor modules, which are coded last.

Incremental testing


100-MAINMODULE

210-WAGEROUTINE

HIERARCHY OR STRUCTURE CHARTHIERARCHY OR STRUCTURE CHART Structure charts illustrate the logic flow in a

program.The following chart shows the relationships among modules in a program:

200-INITIALIZE


RULES FOR INTERPRETING PSEUDOCODERULES FOR INTERPRETING PSEUDOCODE

1. Each block on the Hierarchy chart needs to be represented in pseudocode

2. Paragraph names are prepared in numerical sequence 100-Main-Module 200-Initialize 210-Wage-Routine 220-Finalize-Program Etc…

3. The instructions between the:PERFORM UNTIL NO MORE DATA

executed repeatedly UNTIL there are no more records to process

END-PERFORM.


Divisions of a Cobol ProgramDivisions of a Cobol Program Identification Division

Identifies program to OSProvides documentation

Environment DivisionDefines filesEstablishes Logical (program) and physical (computer) relationship

Data DivisionDescribes all input and output dataAs well as scratch pad data (working storage)

Procedure DivisionAll the program logic


1 IDENTIFICATION DIVISION.2 PROGRAM-ID. SENIOR.3 AUTHOR. ROBERT GRAUER.45 ENVIRONMENT DIVISION.6 INPUT-OUTPUT SECTION.7 FILE-CONTROL.8 SELECT STUDENT-FILE ASSIGN TO ‘A:\CHAPTR02\SENIOR.DAT’9 ORGANIZATION IS LINE SEQUENTIAL.10 SELECT PRINT-FILE11 ASSIGN TO PRINTER.1213 DATA DIVISION.14 FILE SECTION.15 FD STUDENT-FILE16 RECORD CONTAINS 43 CHARACTERS17 DATA RECORD IS STUDENT-IN.18 01 STUDENT-IN.19 05 STU-NAME PIC X(25).20 05 STU-CREDITS PIC 9(3).21 05 STU-MAJOR PIC X(15).22

Identification Division

Data Division

Environment Division

Figure 1.6 The First COBOL Program


23 FD PRINT-FILE24 RECORD CONTAINS 132 CHARACTERS25 DATA RECORD IS PRINT-LINE.26 01 PRINT-LINE PIC X(132).2728 WORKING-STORAGE SECTION. 29 01 DATA-REMAINS-SWITCH PIC X(2) VALUE SPACES.3031 01 HEADING-FILE.32 05 FILLER PIC X(10) VALUE SPACES. 33 05 FILLER PIC X(12) VALUE ‘STUDENT NAME’.34 05 FILLER PIC X(110) VALUE SPACES.3536 01 DETAIL-LINE.37 05 FILLER PIC X(8) VALUE SPACES.38 05 PRINT-NAME PIC X(25).39 05 FILLER PIC X(99) VALUE SPACES.40

Data Division

Figure 1.6 The First COBOL Program (continued)


41 PROCEDURE DIVISION. 42 100-PREPARE-SENIOR-REPORT. 43 OPEN INPUT STUDENT-FILE 44 OUTPUT PRINT-FILE 45 READ STUDENT-FILE 46 AT END MOVE ‘NO’ TO DATA-REMAINS-SWITCH47 END-READ 48 PERFORM 200-WRITE-HEADING-LINE 49 PERFORM 210-PROCESS-RECORDS50 UNTIL DATA-REMAINS-SWITCH = ‘NO’51 CLOSE STUDENT-FILE52 PRINT-FILE

42 53 STOP RUN.54 55 200-WRITE-HEADING-LINE.56 MOVE HEADING-LINE TO PRINT-LINE57 WRITE PRINT-LINE.58 59 210-PROCESS-RECORDS.60 IF STU-CREDITS > 110 AND STU-MAJOR = ‘ENGINEERING’61 MOVE STU-NAME TO PRINT-NAME62 MOVE DETAIL-LINE TO PRINT-LINE63 WRITE PRINT-LINE64 END-IF

43 65 READ STUDENT-FILE66 AT END MOVE ‘NO’ TO DATA-REMAINS-SWITCH67 END-READ.

Figure 1.6 The First COBOL Program (continued)

Procedure Division

End End

Introduction Cobol

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