Understanding the Mainline Logical Flow Through a Program (continued)

1
Understanding the Mainline Logical Flow Through a
Program (continued)

• Procedural program one procedure follows another
  from beginning to end
• Mainline logic has three distinct parts
• Housekeeping steps to get ready
• Main loop instructions executed for every input
  record
• End-of-job steps taken at end of program
• Break the logic down into at least three modules

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Understanding the Mainline Logical Flow Through a
Program (continued)
3
Understanding the Mainline Logical Flow Through a
Program (continued)

• Modularization of the program
• Keeps the job manageable
• Allows multiple programmers to work
  simultaneously
• Keeps the program structured

4
Housekeeping Tasks

• Housekeeping tasks include all steps that occur
  at the beginning of the program
• Declare variables
• Open files
• Perform one-time-only tasks such as printing
  headings
• Read the first input record

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Declaring Variables

• Assign identifiers to memory locations
• Specify the name and data type
• Use meaningful names and follow standards
• Prefixes may be used to group related variables
• Declare a variable for each field in a data file

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Declaring Variables (continued)

• Initializing (or defining) the variable
  providing an initial value
• Some languages provide default initial values
• Other languages leave variables with an unknown
  or garbage value
• Variables representing data fields in files do
  not need to be initialized

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Declaring Variables (continued)

• Can use variables for report headings
• Embed any required spaces
• Heading can be printed using these variables

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Declaring Variables (continued)

• Local variables declared within a module
• Global variables declared at the beginning of
  the program, and used in all modules
• Annotation box flowchart symbol containing notes
• Data Dictionary list of variables used in a
  program, with their type, size, and description

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Opening Files

• Specify file name and path (location)
• Issue a file open command
• If no input file is opened, input may be accepted
  from the standard input device (e.g., keyboard)
• You must open both input and output files to be
  used, including printer output device
• If no output file is opened, standard output
  device (e.g., monitor) may be used

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Printing Headings

• Printing headings for reports usually is done at
  beginning of the program or possibly for each new
  page

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Reading an Input Record

• Reading the first input record is the last
  housekeeping task
• Interactive application
• Interacts with users via keyboard or mouse input
• Program pauses when the read command is executed
  until the user enters data
• Delimiter a character designated as a separator
  between data values
• Prompt an output statement that asks the user to
  enter specific data

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Reading the First Input Record (continued)

• Interactive input (from a keyboard)

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Reading an Input Record

• Input from a data file

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Checking for the End of the File

• After reading a file
• For an interactive program, EOF may be determined
  when
• User enters a predetermined sentinel value
• User selects a screen option using a mouse
• For input from a file, the input device
  recognizes EOF
• EOF may occur on the first read
• If there is data, each record is processed before
  the next read occurs

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Checking for End of File (continued)
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Modules, Subroutines, Procedures, Functions, or
Methods

• Module
• Unit of code that performs one small task
• Called a subroutine, procedure, function, or
  method
• Modularization breaking a large program into
  modules

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Modules, Subroutines, Procedures, Functions, or
Methods (continued)

• Advantages of modularization
• Provides abstraction
• Allows multiple programmers to work
  simultaneously
• Allows code reuse
• Makes identifying structures easier

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Modularization Provides Abstraction

• Abstraction
• Focusing on important properties while ignoring
  non-essential details
• Avoids the low-level details and uses a
  high-level approach
• Makes complex tasks look simple

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Modularization Provides Abstraction (continued)

• A To-Do list
• with abstraction without abstraction

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Modularization Allows Multiple Programmers to
Work on a Problem

• Large programming projects can be divided into
  modules
• Modules can be written by different programmers
• Development time is significantly reduced

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Modularization Allows You to Reuse Your Work

• Reusability the ability to use modules in a
  variety of applications
• Reliability assurance that a module has been
  tested and proven to function correctly

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Modularizing a Program

• Most programs contain a main module
• Contains the mainline logic
• Accesses other modules or subroutines
• Rules for module names used here
• Must be one word
• Should be meaningful
• Are followed by a set of parentheses

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Modularizing a Program (continued)

• Calling program (or calling module) one that
  uses another module
• Flowchart symbol for calling a module a
  rectangle with bar across the top
• Flowchart for the module contains
• Module name in the start symbol
• exit or return in the stop symbol
• When a module is called, logic transfers to the
  model
• When module ends, logic transfers back to the
  caller

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Modularizing a Program (continued)
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Modules Calling Other Modules
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Understanding Documentation

• Documentation
• All supporting material that goes with a program
• Two major categories for users and for
  programmers
• Usually created by system analysts and/or tech
  writers
• May be printed or electronic (Web or CD)
• End users people who use computer programs
• Program Documentation
• Internal program documentation comments within
  code
• External program documentation supporting
  paperwork written before programming begins

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Completing the Documentation

• Program documentation may contain
• Output design
• Input description
• Flowcharts
• Pseudocode
• Program code listing
• User documentation may contain
• Manuals
• Instructional material
• Operating instructions