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)
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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
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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 nonessential 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
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