programming logic and design fifth edition, comprehensive

Programming Logic and Design

Fifth Edition, Comprehensive

Chapter 3The Program Planning Process:

Documentation and Design

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Objectives

• Learn about documentation

• Learn about the advantages of modularization

• Learn how to modularize a program

• Declare local and global variables and constants

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Objectives (continued)

• Understand the mainline logic for many procedural programs

• Create hierarchy charts

• Understand the features of good program design

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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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Output Documentation

• Describes the results the user can see when a program is complete

• Usually written first

• Planning done in consultation with the end user

• After desired output is known, programmer can plan processes needed to produce output

• Most common types of output:– Printed reports– Screen output

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Designing Printed Reports

• Printed reports: designed using a print chart

• Created using word-processor or design software

• Printed reports may contain:– Detail lines: display data details– Heading lines: contain title and column headings– Total (or summary) lines: contain statistics or end of

report indicators

• Printed reports may contain only summary information

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Designing Screen Output

• Program output may appear on a monitor screen

• In a GUI, user sees a screen and can interact with a mouse or pointing device

• Output design resembles a sketch of a screen

• GUI designed to allow user to scroll through records

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Designing Screen Output (continued)

Figure 3-2 Inventory records displayed in a GUI environment

Figure 3-3 Inventory records displayed in a running program

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Input Documentation

• Describes what input is available to produce the output

• File description: – Describes data stored in a file– Indicates fields, data types, and lengths

Figure 3-6 Inventory file description

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Input Documentation (continued)

• Input files organized in different ways– Field may occupy exactly 15 characters for each record

• Adding characters to the end of a data field to force it to a specified size is padding the field

• Some names might be truncated or abbreviated– Fields may be delimited

• Delimiter: character that separates fields– Numeric fields may occupy a specified number of bytes

• One program variable for each field• Each data field declared using the data type indicated

in the file description

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Input Documentation (continued)

• Programmers need to know:– Data file name– Data fields and their order within the file– Data types of each field

Figure 3-7 Plan for discounted prices report

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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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Completing the Documentation (continued)

• User documentation:– Written clearly in plain language– Usually prepared by system analysts and/or tech

writers

• User documentation usually indicates:– How to prepare input– Output distribution and interpretation– Error message information– Run frequency

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Understanding the Advantages of Modularization

• Module: – Unit of code that performs one small task– Called a subroutine, procedure, function, or method

• Invoke (call) a method is to execute it• Calling method invokes the called method• Program contains unlimited number of methods

– Each method can be called unlimited number of times

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Understanding the Advantages of Modularization (continued)

• Modularization: breaking a large program into modules

• 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

• Focuses on important properties while ignoring non-essential details

• Avoids low-level details

• Makes complex tasks look simple

• High-level programming languages allow English-like vocabulary– One statement corresponds to dozens of machine

instructions

• Modules provide another way to achieve abstraction

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Modularization Provides Abstraction (continued)

• To-do list with abstraction

Do laundryCall Aunt NanStart term paper

• To-do list without abstraction

Pick up laundry basketPut laundry basket in

carDrive to laundromatGet out of car with

basketWalk into laundromatSet basket down. . .

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Modularization Allows Multiple Programmers to Work on a Problem

• Commercial programs rarely written by a single programmer

• Development time is significantly reduced• Large programming projects can be divided into

modules• Modules can be written by different programmers or

programming teams

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Modularization Allows You to Reuse Your Work

• Subroutines that are useful should be used more than once in a program– Example: routine that checks the current date

• Instructions placed in their own module are easy to port to other applications

• Reusability: the ability to use modules in a variety of applications

• Reliability: assurance that a module has been tested and proven to function correctly

• Reliable software saves times and money

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Modularizing a Program

• Most programs contain a main program– Contains the mainline logic– Accesses other modules or subroutines

• Rules for naming modules different for every programming language– For this text:

• Must be one word

• Should be meaningful

• Followed by a set of parentheses

• Corresponds to module naming in Java, C++, C#

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Modularizing a Program (continued)

Table 3-1 Suggested identifiers for a module that calculates an employee’s gross pay

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Modularizing a Program (continued)

• Calling program (or calling module): one that uses another module

• Flowchart symbol for calling a module: rectangle with bar across the top

• Flowchart for the module– Start symbol: contains module name

– Stop symbol: contains exit or return

• 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)

Figure 3-8 Sample logic Figure 3-9 Logic from Figure 3-8 using a method

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Modularizing a Program (continued)

Figure 3-10 Logic from Figure 3-9 using two methods

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Modularizing a Program (continued)

• Method is encapsulated in another method if it is contained in another method

• Knowing when to break a module into its own subroutines or submodules is an art

• Best practice: place together statements that contribute to one specific task

• Functional cohesion: extent to which the statements contribute to the same task

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Declaring Local and Global Variables and Constants

• Arguments: data items required by a method• Returning a value: data sent back by a method• Method must include:

– Header: includes method identifier, other identifying information

– Body: contains all statements in the method– Return statement: marks the end of the method

• Returns control to the calling method

• Data items are visible only within the method in which they are declared

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Declaring Local and Global Variables and Constants (continued)

Figure 3-12 Program that prints a bill using main program that calls nameAndAddress() method

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Declaring Local and Global Variables and Constants (continued)

• Variables and constants are in scope only within method in which they are declared– Variables and constants are local to the method

• Global variables and constants are known to the entire program

• Variables and constants declared outside any method are declared at the program level

• Reasons to declare variables globally:– Needed in many methods throughout a program– Declare class’s data fields at class level

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Declaring Local and Global Variables and Constants (continued)

• Declaring global variables and constants: violates encapsulation

• Declaring variables and constants within methods: methods are portable

• When two or more methods require access to same data, pass the data between methods

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Declaring Local and Global Variables and Constants (continued)

Figure 3-15 Program that prints a bill with some constants declared globally

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Understanding the Mainline Logic for Many Procedural Programs

• Mainline logic of most procedural programs follows same general structure:– Housekeeping tasks

• Variable and constant declarations

• Opening files

– Main loop tasks• Processes that must occur for every data record

– End-of-job tasks• Print footer lines

• Close open files

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Understanding the Mainline Logic for Many Procedural Programs (continued)

Figure 3-16 Flowchart and pseudocode of mainline logic for a typical procedural program

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Understanding the Mainline Logic for Many Procedural Programs (continued)

Figure 3-17 Sample payroll report

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Figure 3-18 Logic for payroll report

Understanding the Mainline Logic for Many Procedural Programs (continued)

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Creating Hierarchy Charts

• Hierarchy chart: – Illustrates modules’ relationships– Tells which routines call which other routines– Does not tell when or why the modules are called

Figure 3-19 Hierarchy chart program in Figure 3-16

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Creating Hierarchy Charts (continued)

Figure 3-20 An organizational hierarchy chart

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Creating Hierarchy Charts (continued)

Figure 3-21 Billing program hierarchy chart

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Features of Good Program Design

• As programs become larger, need for planning and design increases

• Follow expected and clear naming conventions

• Store program components in separate files

• Strive to design clear statements within your programs and modules

• Maintain good programming habits

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Following Naming Conventions

• Use meaningful names– Self-documenting: program code explains itself to

readers without further documentation – Pronounceable names– Use abbreviations carefully

• Avoid digits in a name

• Separate words in long, multiword variables

• Use is or are in names for variables that hold status

• Name constants in all uppercase

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Storing Program Components in Separate Files

• Modularization helps to organize programs

• Storing all modules in program file leads to very large program files

• Store modules in individual files– Use include, import, copy statement

• Share the compiled version of the code, not the source code

• Implementation hiding: hiding the details of how a program works

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Storing Program Components in Separate Files (continued)

Figure 3-22 Partial EMPLOYEES file description

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Storing Program Components in Separate Files (continued)

Figure 3-23 Data fields in Figure 3-22 defined in the C++ language

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Designing Clear Statements

• Select good identifiers

• Avoid confusing line breaks

• Use temporary variables to clarify long statements

• Use constants where appropriate

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Avoiding Confusing Line Breaks

• Provide enough line breaks for clarity

Figure 3-24 Code segment with insufficient line breaks

Figure 3-25 Code segment with appropriate line breaks

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Using Temporary Variables to Clarify Long Statements

• Use temporary variable (work variable) to hold intermediate mathematical results

• Easier to see calculations if computation is broken into individual steps

Figure 3-26 Two ways of achieving the same salespersonCommission result

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Using Constants Where Appropriate

• Use named values wherever possible

• Easier for readers to understand

• When value changes, make one change where constant is defined

• Prevents typographical errors

• Values of constants will not change during execution of the program

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Maintaining Good Programming Habits

• Every program will be better if planned before coded

• Maintain habit of first drawing flowchart or pseudocode

• Walk through program logic on paper (desk-checking) before programming

• Think carefully about variable and module names

• Design program statements for readability

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Maintaining Good Programming Habits (continued)

Figure 3-27 Program that uses named constants

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Summary

• Documentation: all supporting material for a program

• Output documentation: includes report designs

• File description: details data types and lengths of each field of data in the file

• User documentation: manuals and instructional materials, and operating instructions

• Modules: smaller, reasonable units of code that provide reusability – Subroutines, procedures, functions, methods

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Summary (continued)

• Modularization:– Provides abstraction– Allows multiple programmers to work on a problem– Makes it easy to reuse work and identify structures

• Modules can call other modules– Flowchart symbol is a rectangle with a bar across

the top

• Variable declarations define the name and type of the data to be stored

• Hierarchy chart illustrates modules’ relationships

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Summary (continued)

• Common structure for procedural programs:– Housekeeping tasks– Main loop– End-of-job tasks

• Hierarchy chart illustrates modules’ relationships

• As programs become larger, need for good planning increases– Store program components in separate files– Use meaningful names– Avoid confusing line breaks, long statements