ch05_97

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PowerPoint Presentation:

Richard H. Baum, Ph.D.DeVry Institute of Technology

9th Edition

Structured COBOLProgramming

Nancy Stern

Hofstra University

Robert A. Stern

Nassau Community

College

Copyright @ 2000 John Wiley & Sons, In. All rightsreserved. Reproduction or translation of this work beyond

that permitted in Section 117 of the 1976 United StatesCopyright Act without the express permission of thecopyright owner is unlawful. Request for further informationshould be addressed to the permissions Department , JohnWily & Sons, Inc. The purchaser may make back-up copiesfor 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 programsor from the use of the information contained herein.

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Structured COBOL Programming, Stern & Stern, 9th Edition

CHAPTER 5DESIGNING and DEBUGGINGBATCH and INTERACTIVECOBOL PROGRAMS

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OBJECTIVES

To Familiarize You With:

1. The way structured programsshould be designed.

2. Pseudocode and flowcharts asplanning tools used to map out thelogic in a structured program.

3. Hierarchy or structure charts asplanning tools used to illustrate therelationships among modules in atop-down program.

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OBJECTIVES

4. The logical control structures ofsequence, selection, iteration, andcase.

5. Techniques used to make programseasier to code, debug, maintain, andmodify.

6. Interactive processing.

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CONTENTS

What Makes a Well-DesignedProgram?

Designing Programs beforeCoding Them

Illustrating Logical Control

Structures Using Pseudocodeand Flowcharts

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CONTENTS

Hierarchy Charts for Top-DownProgramming

Naming Modules or Paragraphs

Modularizing Programs

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CONTENTS

A Review of Two CodingGuidelines

An Introduction to InteractiveProcessing

Debugging Programs

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WHAT MAKES A WELL-DESIGNED PROGRAM?

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Program Logic Should BeMapped Out Using a PlanningTool The term program design means the

development of a program so that itselements fit together logically and in

an integrated way.

If programs are systematicallyplanned before they are coded, they

will be better designed.

Planning tools such as pseudocode,flowcharts, and hierarchy charts help

map out program logic.

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PROGRAMS SHOULD BE STRUCTURED

Well-designed, structured programsare those that have a series oflogical constructs.

Thus, the order in which theseinstructions are executed isstandardized.

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PROGRAMS SHOULD BE STRUCTURED

Each set of instructions that performs aspecific function is defined in a module orprogram segment.

A module is also called a routine or, in COBOL,a paragraph.

Each module is executed in its entirety from

specific places in a program.

In COBOL, modules are executed using aPERFORM statement.

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PROGRAMS SHOULD USE A TOP-DOWN APPROACH

The modules are coded in a hierarchicalorder, with main modules written firstfollowed by secondary modules that

include the detailed code. The coding of modules in a hierarchical

manner is called top-down programming.

This top-down approach is some times calledstepwise refinement.

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DESIGNING PROGRAMSBEFORE CODING THEM

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HOW PROGRAMS ARE DESIGNED

In addition to learning syntax

programmers must learn how todesign a program so that it functionseffectively as an integrated whole.

The techniques for developing well-designed programs are applicable toall languages.

Once you know how to design programsefficiently and effectively, you need onlylearn the syntax rules of a specificlanguage to implement these design

elements.

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Two tools for planning the logic to beused in a program are pseudocodeandflowcharts.

These should be used before the program iscoded.

PSEUDOCODE AND FLOWCHARTS

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PseudocodeA pseudocode is a set of statements that

specifies the instructions and logical control

structures that will be used in a program.

Flowcharts A flowchart is a diagram or pictorial

representation of the instructions and logicalcontrol structures that will be used in aprogram.


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Pseudocode Pseudocode has been designed

specifically for representing the logic in astructured program.

The pseudocode for a program thatreads in two numbers, adds them,and prints the total is as follows:

START

READ AMT1, AMT2

COMPUTE TOTAL = AMT1 + AMT2

WRITE TOTAL

STOP

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Flowcharts

The following symbols are the ones mostfrequently used.

Symbol Name Use

Input/Output Usedfor all I/Ooperations

Processing Used for allarithmeticand datatransfer

operations.

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Flowcharts

The following symbols are the ones mostfrequently used.

Symbol Name Use

Decision Used totest for acondition.

Terminal Used toindicate the

beginning and end ofa program or module.

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Flow Charts (continued)Symbol Name Use

Connector Used to

indicate thepoint at which a

transfer of controloperation occurs.

Predefined Used toProcess indicate the

name of a module

to be executed.

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FLOWCHARTING CONVENTIONS

1. Each symbol denotes a type of operation.2. A note is written inside each symbol to

indicate the specific function to be performed.

3. The symbols are connected by flowlines.

4. Flowcharts are drawn and read from top tobottom unless a specific condition is met thatalters the path.

5. A sequence of operations is performed until a

terminal symbol designates the sequence'send or the end of the program.

6. Sometimes several steps or statements arecombined in a single processing symbol forease of reading.

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Flow Chart

Example:

STARTREAD

AMT1,

AMT2COMPUTE

TOTAL =

AMT1 + AMT2

WRITETOTAL

STOP

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PSEUDOCODE ANDFLOWCHARTS

Flow Chart Example

This sequence of instructions is called amodule.

The flowchart is read from top to bottom.

Since there is no need to repeat

instructions or to test for any conditions,this simple flowchart indicates that twonumbers will be read, added together,and the sum printed.

THE FOUR LOGICAL CONTROL

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THE FOUR LOGICAL CONTROLSTRUCTURES

Structured programs use logical controlstructures to specify the order in whichinstructions are executed.

These structures are the same for alllanguages.

LOGICAL CONTROL STRUCTURES

1. Sequence.

2. Selection.

3. Iteration.

4. Case Structure.


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SEQUENCE A sequence is instructions executed in the

order they appear.

The following pseudocode examplerepresents a sequence.

The ellipses mean that each statement hasother components.

We use a sequence to depict the logicwhen data is to be processed in a step-by-step order.

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SEQUENCE: A PSEUDOCODE EXAMPLE

START (OR ENTRY)

.

.

.

ADD ...WRITE

STOP (OR RETURN)

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SEQUENCE: Beginning and Ending Modules

All modules or sequences in a pseudocodeand a program flowchart should be clearly

delineated.

The pseudocode could use START and STOPas code words to delimit a sequence ormodule, particularly the main module.

Each instruction in a structured program isexecuted in sequence unless another logicalcontrol structure is specified.

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Selection

Selection is a logical control constructthat executes instructions depending on

the existence of a condition. It is sometimes called an IF-THEN-ELSE

logical control structure.

If the condition is true (or exists), thestatement or statements following theTHEN statement are executed.


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Selection

If the condition does not exist (or isfalse), we execute the statement orstatements following the ELSE statement.

Later we will see that a COBOL 85program can look just like pseudocode.


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Iteration

The structure that makes use of the

PERFORM UNTIL is called iteration. Iteration or looping is a logical control

structure used for specifying the repeated

execution of a series of steps.An example follows.


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Iteration: a COBOL 85 examplePERFORM UNTIL

PERFORM

UNTILARE-THERE-MORE-RECORDS='NO

.

.

.

END-PERFORM


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Case Structure

The case structure is a special control

structure used when there are numerouspaths depending on the contents of agiven field.

It is used when we wish to perform one of

several possible procedures depending onsome condition or value.


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Case Structure The case structure is animportant construct for processing menusinteractively and for helping to minimize

errors through data validation. The procedure or module to be executed

depends on the actual value of the entrymade by the user.


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Case Structure: A Pseudocode Example

EVALUATE UPDATE-CODE

WHEN 1

PERFORM UPDATE

WHEN 2

PERFORM NEW-HIRE

WHEN OTHERPERFORM ERROR

END-EVALUATE

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PSEUDOCODE RULES

1. Pseudocode is written and read from topto bottom.

2. The logical control structure is definedwith the use of key terms:

PERFORM . . . END-PERFORM

IF-THEN-ELSE . . . END-IF

CASE . . . END-CASE.

3. The operations to be executed within aPERFORM, IF-THEN-ELSE, or CASE(EVALUATE) can be coded in-line or in aseparate module.

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FLOWCHART RULES

1. A flowchart is drawn and read from topto bottom unless a specific conditionalters the path.

2. The symbol itself denotes the type ofoperation such as input/output orprocessing.

3. An explanatory note within the symboldescribes the specific operation to beperformed.

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HIERARCHY CHARTSFOR TOP-DOWN

PROGRAMMING

HIERARCHY CHARTS

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HIERARCHY CHARTS

A hierarchy or structure chart is a graphic

method for segmenting a program intomodules.

Its main purpose is to provide a visual

overview of the modules in a program.

You will need to plan the logic in twoways:

(1) with pseudocode (or a flowchart) toillustrate the logical structure, and

(2) with a hierarchy chart to illustrate howmodules should relate to one another.

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HIERARCHY CHARTS

1. A hierarchy chart represents programmodules as rectangular boxes andillustrates the interrelationships among

these modules with the use of connectedlines.

2. A module is a well-defined program

segment that performs a specificfunction.

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EXAMPLE OF A HIERARCHY CHART

A

B C

D EF G H

HIERARCHY CHART

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HIERARCHY CHARTEXPLANATION (1 of 2)

The letters A through H representparagraph-names that are executed withthe use of a PERFORM as follows:

A.PERFORM B.

PERFORM C.

B.

PERFORM D.

PERFORM E.

HIERARCHY CHART

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HIERARCHY CHARTEXPLANATION (2 of 2)

C.

PERFORM F.

PERFORM G.

PERFORM H.

The hierarchy chart only illustrates

modules executed from other modules. Each block or box in a hierarchy chart

represents a module.

HIERARCHY CHARTS

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HIERARCHY CHARTS

ADVANTAGES OF A HIERARCHY OR

STRUCTURE CHART

1. It helps programmers, systemsanalysts, and users see how modulesinterrelate.

2. It helps programmers debug and

modify programs.

3. It helps programming managersassess the efficiency of programs.

NAMING MODULES OR

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NAMING MODULES ORPARAGRAPHS

A module or set of relatedinstructions is equivalent to aparagraph.

Use a standard method for namingparagraphs in all programs.

Choose meaningful names.

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MODULARIZING PROGRAMS

We have seen that top-down programsare written with main units or modulesplanned and coded first, followed by more

detailed ones.

Structure or hierarchy charts illustratethe relationships among these modules.

Statements that together achieve a given taskshould be coded as a module.

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A REVIEW OF TWOCODING GUIDELINES

CODE EACH CLAUSE ON A

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CODE EACH CLAUSE ON ASEPARATE LINE

Coding one clause per line makesprograms easier to read and debug.

Words and clauses can be separated withany number of blank spaces.

Having only one clause on each line helps

to isolate errors.

INDENT CLAUSES WITHIN A

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INDENT CLAUSES WITHIN ASTATEMENT

Indentation makes programs easierto read.

In general, we indent four spaces oneach line.

Indentation is used to clarify the

logic.Note, however, that indentation does

not affect the program logic at all.

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DEBUGGING TIP

COBOL 85 programmers should alwaysuse scope terminators with the READ andIF statements.

When scope terminators are coded, periodsare not used to end statements except for thelast statement in a paragraph.

Scope terminators ensure that all clauseswithin a statement will be associatedwith the appropriate instruction, therebyminimizing logic errors.

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AN INTRODUCTION TOINTERACTIVE

PROCESSING

INTERACTIVE PROCESSING

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COBOL was originally developed toprocess files of data and is still widelyused for that purpose.

Many organizations, however, are usingCOBOL for interactive processing where--

the user enters data using a keyboard on a PCor a terminal, and

output is displayed on the monitor at theusers desk.

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We use theACCEPT verb for enteringinput from a keyboard and the DISPLAYverb for displaying output on a screen.

The instructionACCEPTidentifier enables the

user to enter input data directly from akeyboard rather than from a disk file.

The identifier is likely to be a WORKING-

STORAGE entry.

When input is entered using theACCEPTverb, there is no need to establish a file.


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To enter as input a DISCOUNT-AMT, forexample, you can code:

ACCEPTDISCOUNT-AMT

The format is determined by the PIC clausefor DISCOUNT-AMT.

WORKING-STORAGE SECTION.

01 DISCOUNT-AMT PIC 9(3).

Using a keyboard, the use would enter threeintegers into DISCOUNT- AMT.

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DEBUGGING PROGRAMS

After you design a program you areready to code it.

Programs must be fully tested toensure that there are no errors.

The process of eliminating errorsfrom a program is called debugging.

SYNTAX ERRORS

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SYNTAX ERRORS

After a program has been planned andcoded, it is keyed into a computer. Then itis ready to be compiled or translated intomachine language.

During this translation/compilation process,the compiler will list any violations inprogramming rules that may have occurred.

These rule violations are called syntaxerrors; they must be corrected before theprogram can be executed.

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SYNTAX ERRORS

When diagnostics appear in a sourcelisting (either at the end or right after theline in question), they typically have thefollowing format:

Line No. Error Code Error Message

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PC COMPILERS

Micro Focus and RM/COBOL-85 havecompiler-generated messages similar tothose just discussed.

Micro Focus will highlight the word anddisplay the error messages.

On-line HELP is available to further explainthe meaning of the messages. These errorcodes are documented in its On-Line-Reference Guide.

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LOGIC ERRORS

Syntax errors are detected by thecompiler and, except for warnings, theyshould all be corrected before you run theprogram.

However, even after a program has beencompiled so that it has no syntax errors itis not yet fully debugged.

The program must be executed with testdata to ensure that there are no logicerrors.

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LOGIC ERRORS

Some logic errors result in a programinterrupt.

These are called run-time errors, and must be

corrected before execution can continue.

Other logic errors result in erroneousoutput.

These will be detected only if the test data iscomplete and the program is carefullychecked by the programmer.

C S S

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CHAPTER SLIDES END HERE

CHAPTER SUMMARY COMES NEXT

CHAPTER SUMMARY

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CHAPTER SUMMARY

I. Program Design

A. Logical Control Structures

The logical control structures are asfollows:

1. Sequence

2. IF-THEN-ELSE or Selection

3. Iteration Using a PERFORM UNTIL . . .END-PERFORM loop

4. Case Structure

CHAPTER SUMMARY

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CHAPTER SUMMARY

B. Program Planning Tools

1. To structure a program, use pseudocode or aflowchart.

2. To illustrate the top-down approach showing

how modules interrelate, use a hierarchychart.

C. Naming Modules

Use descriptive names along with numericprefixes that help locate the paragraphsquickly (e.g., 200-PRINT-HEADING,

500-PRINT-FINAL- TOTAL).

CHAPTER SUMMARY

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CHAPTER SUMMARY

D. A Well-Designed Program Uses:

1. Structured programming techniques.

2. A modularized organization.

3. A top-down approach: Code main modules first, followed by

minor ones.

4. Meaningful names for fields andparagraphs.

5. One clause per line and indentedclauses within a sentence.

CHAPTER SUMMARY

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CHAPTER SUMMARY

II. Interactive Processing

A. You can useACCEPT to input

data from a keyboard.B. You can use DISPLAYto output

information to a screen.

CHAPTER SUMMARY

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CHAPTER SUMMARY

III. Debugging

A. Correct all syntax errors or ruleviolations that are listed by thecompiler.

B. Test your program carefully with testdata that includes all possible values

that the program might encounterduring a normal production run.

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