Structured COBOL Programming

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Structured COBOL Programming

• _at_ IUP
• Computer Science Department
• Text by
• Shelly, Cashman, Foreman
• Notes by
• Dr. William W. Oblitey

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Introduction to COBOL and Program Development

• Chapter Objectives
• Identify the Advantages and Disadvantages of
  COBOL
• Understand the difference between record input
  and output
• List the steps required by the Programming
  Process
• Name the Logic Structures used in a Structured
  Program

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Chapter Objectives

• Describe Top-down Design and Top-down Programming
• Name the four divisions of a COBOL program
• Specify the purpose of each COBOL division
• Identify valid COBOL words
• Describe the format of a line of COBOL source code

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Introduction

• COBOL
• Common Business Oriented Language
• First released in 1960 by CODASYL
• Conference of Data Systems Language
• Purpose was to provide a High-Level Programming
  Language for the business world.

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High-Level Vs. Low-Level Languages

• High-Level Language
• The program statements are not closely related to
  the internal characteristics of the machine.
• Are more English-like and less cryptic
• Can be easily transferred from one
• Examples
• COBOL, C, C, Java, VB, etc.

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High vs. Low-Level Languages

• Low-Level Language
• Uses symbolic notation to represent machine
  instructions
• Is closely related to the internal architecture
  of the machine
• Cannot be transferred from, one machine system to
  another
• Examples
• Machine language, Assembly language

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COBOLs Survival

• COBOL is widely accepted
• Has been in use for over 35 years
• Many businesses have great investment in COBOL
  programs.
• COBOL is available on every computer platform
• Object-COBOL is available
• COBOL Versions 68, 74, 85, 90?

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Advantages of COBOL

• COBOL was designed to be machine-independent,
  English-like, and self-documenting
• COBOL has had ANSI support since 1960
• ANSI
• American National Standards Institute
• COBOL Compiler
• Translates COBOL source code into machine
  language

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Disadvantages of COBOL

• COBOL programs are wordy
• They are longer than those produced in most other
  languages
• Is not popularly employed for coding scientific
  applications

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Information Processing

• Information Processing
• The production of information by processing data
  on a computer.
• Stream Input/Output
• This is typical with C, Java, VB, etc
• Program reads data and assigns it to variables
• Record Input/Output
• This is typical with COBOL
• COBOL groups data into fields and records
• (See Fig. 1, pg. 4)

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Record Blocking

• Increases the efficiency of record I/O
• Blocking
• Grouping the records transmitted from secondary
  memory to the CPU as needed by the program
• Records are supplied one at a time to the program
  through READ statements
• The block is a physical record and each record
  within the block is a logical record

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Steps in the Programming Process

• Understand the Problem
• Design the Program
• Code the Program
• Test the Program
• Document the Program

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Step 1 - Understanding the Problem

• Be sure that you have a complete understanding of
  the purpose of the program
• read the specifications
• Establish and maintain a channel of communication
  with the client
• Determine what the output of the program should
  be
• Examine the input
• Determine what mathematical calculations are
  needed

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Step 2 - Design the Program

• Develop the sequence of steps you will need to
  solve the problem
• Should not involve a computer
• Tools needed are spacing chart, flowcharts,
  hierarchy charts, and pseudocode.
• Make use of the top-down design approach to
  problem solving

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Step 2 -- Design Tools

• Spacing chart
• Consists of rows and columns that can be used to
  design the appearance of a screen or a printed
  report
• Flowchart
• A graphical representation of the steps needed to
  solve a problem
• Hierarch chart
• Demonstrates the relationship between the
  paragraphs used in the program and how the
  solution is organized
• Pseudocode
• An English-like representation of the actions
  needed to solve the problem.

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Step 3 - Coding the Program

• Design the logic and then translate it into COBOL
  code
• Source code
• These are the instructions you write for the
  computer to carry out.
• It is your code before it is translated into
  machine language
• You write source code with a text editor
• A language sensitive editor helps you by placing
  the cursor in the correct column positions and
  pointing out syntax errors
• Syntax errors caused by not using the language
  correctly

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Step 4 - Testing the Program

• After writing the program, you need to compile
  it.
• Compilation
• translating the source code (program) to machine
  code
• This is done by the compiler
• If syntax errors show up, you should correct them
  and recompile until you obtain a clean compile

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Step 5Documenting the Program

• Documentation is necessary to allow people to
  figure out how to use your program and/or fix it
  when future errors show up or modifications are
  necessary.
• Program documentation can take many forms
• External documentation
• Notes and Manuals for other programmers
• Comments lines and meaningful data names
• These help with program readability and enhances
  the self-documenting nature of COBOL code.

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Structured Programming

• Structured programming uses the three basic logic
  control structures
• Sequence, selection, iteration
• A logic control structure is a way in which
  statements in a program can be executed.
• Advantages offered
• Programs appear neater and are more readable
• Reliability and efficiency of programs are
  improved
• Reduces time spent on debugging, testing, and
  modifying programs
• Increases programmer productivity

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Logic Control Structures

• Sequence Structure
• Here, one imperative statement is executed after
  another (Fig. 1-3, pg. 8)
• Imperative statement
• One that demands an action to be executed
• Selection Structure
• Here, code is executed based on the result of a
  condition (Fig. 1-4, pg. 8)
• Iteration (Looping) Structure
• Here, a set of instructions are executed until
  some predetermined condition is met. (Fig. 1-6,
  pg. 9)

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Top-Down Design/Programming

• Methodologies for solving large problems
• Top-Down Design
• Breaks a large, complex problem into smaller,
  less complex units
• Also called Divide and Conquer strategy
• Top-Down Programming
• The high-level modules are coded as soon as they
  are designed. (See fig. 1-8, pg. 11)

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Divisions of a COBOL Program

• All COBOL programs are divided into four
  divisions (see fig. 1-9, pg. 11)
• IDENTIFICATION DIVISION
• ENVIRONMENT DIVISION
• DATA DIVISION
• PROCEDURE DIVISION
• Each division has a function in the overall
  development and execution of the program

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IDENTIFICATION DIVISION

• Provides the computer with basic information
  about the program
• Has only one required entry
• The division header contains the reserved words
  IDENTIFICATION DIVISION
• The reserved word PROGRAM-ID is used to name the
  program.
• The program name is selected by the programmer.
• Periods are required at end of each division .

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IDENTIFICATION DIVISION

• The COBOL language processor looks for periods to
  terminate various elements of the program.
• The asterisk () is used to convey documentation
  in the program.
• Comment
• The is placed in column 7 and is ignored by the
  COBOL compiler. (see Fig. 1-16, pg. 16)

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ENVIRONMENT DIVISION

• This is the most hardware-dependent part of a
  COBOL program
• Defines Input and Output
• Contains the INPUT-OUTPUT SECTION and the
  FILE-CONTROL paragraph.
• The INPUT-OUTPUT SECTION
• Designates the data files that the program uses.
• Each data file is associated with a hardware
  input-output device

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DATA DIVISION

• Defining files, records, and fields
• Also defines variables for use as counters,
  accumulators, and flags
• It is used to describe the data to be processed
  by the program
• Its first two sections are the FILE SECTION and
  the WORKING-STORAGE SECTION.

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The PROCEDURE DIVISION

• Contains the program logic processing steps
• Contains procedures, which are actions to be
  carried out by the program
• It s made up of separate modules called
  paragraphs.
• Statements in the PROCEDURE DIVIDION begin with
  action verbs (see Fig. 1-10, pg. 12)

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The Paragraph Name

• A paragraph name is user-defined.
• It must end with a period.
• No blanks are allowed in the name.
• Hyphens may be used to separate the words that
  make up the paragraph name.
• Recommended to start the name with a module
  level number.
• Following the paragraph name are COBOL statements
  These designate operations to take place and
  thus begin with verbs. (see Fig. 1-11, pg. 13)

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Overall Program Execution

• COBOL statements are not executed directly
• They are converted into machine language
• The statements in the program are called source
  code
• The statements that the computer executes is
  called the object code
• Execution of a program begins with the first
  statement following the PROCEDURE DIVISION and
  continues statement by statement until the end of
  the program is encountered.

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COBOL Coding Format

• The Coding form this is divided into four major
  fields (see fig. 1-13, pg. 14)
• Usage Columns
• Sequence numbers 1 6
• Indicator area (/,,-) 7
• Area A (Headers) 8 11
• Area B (statements) 12 72
• Program identification 73 80

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Program Preparation

• Line numbers in the program are NOT entered by
  the programmer. They are generated by the
  compiler.
• Area A and Area B entries
• Columns 8 11 is area A
• Columns 12 72 is area B
• These columns are significant because COBOL
  entries must start in specific columns.