INTRODUCTION TO STRUCTURED PROGRAM DESIGN IN COBOL

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• Chapter 1
• INTRODUCTION TO STRUCTURED PROGRAM DESIGN IN COBOL

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COMPUTER PROGRAMMINGAN OVERVIEW
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Types of Computer Programs

• COBOL is one of the many languages used to write
  customized applications programs.

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Applications 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.

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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.

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Machine Language Programs

• All programs executed by the computer must be in
  machine language.

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Symbolic Programs

• Symbolic Programs use English-like or symbolic
  instructions.
• These programs must be translated or compiled
  into machine language.
• COBOL is a symbolic programming language used
  for commercial applications.

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THE APPLICATIONS PROGRAM DEVELOPMENT PROCESS
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PROGRAM DEVELOPMENT PROCESS

• 1. Determine Program Specifications
• Program Specifications consist of the following
• Record layout forms to describe the input and
  output
• Printer spacing charts for printed output
• Screen layouts for interactive input/output

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PROGRAM DEVELOPMENT PROCESS

• 2. Design the Program Using Program Planning
  Tools using Common Tools
• Flowcharts
• A block diagram providing a pictorial
  representation of the logic to be used in a
  program
• Pseudocode
• English-like expressions to depict the logic of
  the program
• Hierarchy Charts
• Charts showing relationships among sections in a
  program

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PROGRAM DEVELOPMENT PROCESS

• 3. Code and Enter the Program
• 4. Compile the Program
• The 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.

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PROGRAM DEVELOPMENT PROCESS

• 5. Test the Program
• Programs are tested or debugged to ensure they
  have no errors.
• A logic error is a type of error that the
  programmer may find only when the program is
  tested with sample or test data.
• 6. Document the Program
• Procedure manuals for users and computer
  operators, called documentation, is prepared for
  use by the operating staff for regular production.

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PROGRAM DEVELOPMENT PROCESS

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

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DEBUGGING TECHNIQUES

• Desk Checking
• Reviewing the program before and after keying
• Correcting Syntax Errors
• Using the printed source list of the diagnostic
  messages to find and correct the errors

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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.

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THE NATURE OF COBOL

• COBOL is a Business-Oriented Language
• COBOL, 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 Language
• COBOL is a common programming language available
  on most computers.

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THE NATURE OF COBOL

• COBOL 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 Language
• Because users are able to understand the
  English-like instructions it is considered a
  user-friendly language.

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THE FUTURE OF COBOL

• COBOL is likely to remain an important language
  in the years ahead for three 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.
• 3. It is a very efficient language.

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QUESTIONS?!
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SELF-TEST QUESTIONS

• 1. A program must be in _________ language to be
  executed or run.
• Solution machine

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SELF-TEST QUESTIONS

• 2. Programs are typically written in a _______
  language rather than in machine language because
  __________.
• Solution symbolic
• machine languages are very complex

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SELF-TEST QUESTIONS

• 3. Programs written in a language other than
  machine language must be _______ before
  execution can occur.
• Solution translated or compiled

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SELF-TEST QUESTIONS

• 4. The process of converting a source program
  into machine language is called ___________.
• Solution compilation or translation

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SELF-TEST QUESTIONS

• 5. The program written in a programming language
  such as COBOL is called the ________ program.
• Solution source or applications

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SELF-TEST QUESTIONS

• 6. The object program is the _______.
• Solution set of instructions that has been
  converted into machine language

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SELF-TEST QUESTIONS

• 7. A ______ converts a source program into
  a(n)_____ program.
• Solution compiler or translator program object
  or machine language

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SELF-TEST QUESTIONS

• 8. The errors that are detected during
  compilation denote ______ they are usually
  referred to as ________ errors.
• Solution any violation of programming rules in
  the use of the symbolic programming language
  syntax

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SELF-TEST QUESTIONS

• 9. Before executing a program with test data,
  the logic of the program can be checked manually
  using a technique called a ____________.
• Solution program walkthrough

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SELF-TEST QUESTIONS

• 10. COBOL is an abbreviation
• for _________.
• Solution Common Business Oriented Language

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SELF-TEST QUESTIONS

• 11. COBOL is a common language in the sense
  that ______.
• Solution it can be used on many computers

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TECHNIQUES FOR IMPROVING PROGRAM DESIGN
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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.

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Structured Programming Using Modular Design for
Coding 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

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Structured Programming Using Modular Design for
Coding Paragraphs

• The typical structured program is divided into
  paragraphs or modules, where a main module calls
  in other modules as needed.
• Each module can be tested independently.
• Paragraph, routine, module are used
  interchangeably

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The 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.

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The Top-Down Approach

• 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.

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A BRIEF OVERVIEW OF PROGRAM PLANNING TOOLS
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RULES FOR INTERPRETING PSEUDOCODE

• 1. A pseudocode begins with a START and ends with
  a STOP.
• 2. All instructions are read in sequence.
• 3. The instructions between the
• PERFORM...END-PERFORM are executed repeatedly
  UNTIL there are no more records to process.

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HIERARCHY OR STRUCTURE CHART

• Structure charts identify WHAT each module does,
  and how it relates to other modules.
• The following chart shows the relationships among
  modules in a program

100-MAIN MODULE
200-WAGE ROUTINE
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CHAPTER SLIDES END HERE

• CHAPTER SUMMARY COMES NEXT

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CHAPTER SUMMARY

• A. The Nature of COBOL
• 1. It is the most widespread commercial
  programming language in use today.
• 2. COBOL is the abbreviation for Common Business
  Oriented Language.
• 3. It is an English-like language.

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SUMMARY

• B. Program Preparation and Debugging
• Get program specifications from the analyst or
  prepare them yourself.
• Use planning tools--flowcharts, pseudocode,
  hierarchy charts--for program design.
• Code the program.
• Compile the program and fix syntax errors.
• Test the program using debugging techniques.
• Document the program.

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SUMMARY

• C. Techniques for Improving Program Design
• 1. Structured Programming
• a. Referred to as GO-TO-less programming
• b. Structured programs are subdivided into
  modules or paragraphs.
• 2. Top-Down Programming
• a. Major modules are coded before minor ones.
• B. Similar to developing an outline before
  writing a report.

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SUMMARY

• D. The COBOL Divisions
• Identification Division
• a. Identifies the program to the computer
  system.
• b. May provide some documentation as well.
• c. PROGRAM-ID is the only required entry.
• Environment Division
• Assigns a file-name to each file used.
• Specifies the device that the file will use.

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SUMMARY

• Data Division
• a. Defines describes all input, output work
  area
• b. File-Section
• (1) Each file-name is described in an FD.
• (2) Each record format within every file is an
  01 entry.
• (3) Record fields are described with a PICTURE
  clause that specifies the size type.
• c. Working-Storage Section
• (1) Defines work areas
• (2) An end-of-file indicator is coded here.

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SUMMARY

• COBOL DIVISIONS
• Procedure Division
• a. Subdivided into paragraphs or modules.
• b. Includes all instructions to process input
  and produce output.
• c. All instructions are executed sequence.
• PERFORM...UNTIL... END-PERFORM is a loop.

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SUMMARY

• Procedure Division
• c. All instructions are executed sequence,
  unless there is a loop such as
• PERFORM UNTIL...
• ..
• ..
• END-PERFORM

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SUMMARY

• Procedure Division
• d. Main-module entries
• The following are typical entries in a main
  module
• (1) Files are either INPUT or OUTPUT and
  activated in an OPEN statement.
• (2) A PERFORM... .
  END-PERFORM is a loop that is executed until
  there are no more records.

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SUMMARY

• Main-module entries (continued)
• Within the PERFORM we often code a READ...
  AT END... NOT AT END END-READ.
• (4) A CLOSE statement deactivates all files.
• (5) STOP RUN ends processing.

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SUMMARY

• e. Calculation or processing paragraphs
• (1) These paragraphs are executed when a
  statement in the main module specifies a PERFORM
  paragraph name.
• (2) For example, logic for processing an input
  record may be contained in one or more paragraphs.