Extended Prelude to Programming Concepts & Design, 3/e

byStewart Venit and Elizabeth Drake

Chapter 2:Developing a Program

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2.1 The Program Development Cycle

• Problem solving principles– Completely understand the problem– Devise a plan to solve it – Carry out the plan– Review the results

• Writing a program– 1) Analyze the problem– 2) Design the program– 3) Code the program– 4) Test the program

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1. Analyze the Problem

• Identify desired results (output)• Determine input needed to produce those results• Example: Create a program to generate 6

numbers to play the lottery– Problem must be more specific– Desired results: 6 different positive integers within the

range of 1 to 40

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2. Design the program

• Create a detailed description of program– Use charts or ordinary language (pseudocode)

• Identify algorithms needed– Algorithm: a step-by-step method to solve a problem

or complete a task

• Algorithms must be:– Well defined– Well ordered– Must produce some result– Must terminate in a finite time

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3. Code the program

• Translate charts or pseudocode (ordinary language) into program code

• Add statements to document what the code does– Internal documenation– External documentation

• Each programming language uses its specific syntax

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4. Test the program

• In analysis phase: continually ask questions– Did I interpret data correctly?– Does program fulfill requirements? Etc…

• In design phase: use desk-checking to walk through the program

• In coding phase: software will alert you to errors in syntax

• Finally, check your program with as many sets of test data as possible

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2.2 Program Design• Modular programming

– Determine the major tasks that the program must accomplish. Each of these tasks will be a module.

– Some modules will be complex themselves, and they will be broken into submodules, and those submodules may also be broken into even smaller modules.

– This is called top-down design

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The Sale Price Example

A local department store needs to develop a program which, when given an item’s original price and the percentage it is discounted, will compute the sale price, with sales tax.

Output required:

name of item, discounted price, amount of sales tax, total price

Input required:

name of item, original price, percent discounted

Formulas required:

SalePrice = OriginalPrice – AmountSaved

AmountSaved = OriginalPrice * (DiscountRate/100)

Tax = SalePrice * TaxRate

TotalPrice = SalePrice + Tax

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Top Down DesignThe first illustration of top down design describes

the 3 fundamental tasks that are required in the Sale Price example:

– Input

– Perform Calculations (Process)

– Output

Input Perform Calculations OutputInput variables: AmountSaved = Display:

OriginalPrice * DiscountRate/100 TotalPrice

ItemName SalePrice = OrigialPrice-AmountSaved

DiscountRate Tax = SalePrice * TaxRate

OriginalPrice TotalPrice = SalePrice + Tax

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A Code Module

• Performs a single task• Is self-contained and independent of other

modules• Is relatively short – less than 1 page

• A module is called by the calling module• A call statement causes a called module to be

executed; control is transferred from the calling module to the called module

• The main module is the controller of all sub-modules

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The Hierarchy Chart

• Like an organization chart – shows position of modules in the program.

• Depicts what modules exist and how they are related.

• Large programs need a “map” for documentation.

• One page of code per module – keeps the program manageable.

• We will have very small modules while getting comfortable using these tools.

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Hierarchy Chart

Sample Hierarchy Chart for the Sale Price Program:

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2.3 Coding, Documenting, and Testing

• Coding – Coding is done in a specific programming language. We will use

pseudocode. – This phase should only begin after a solid design exists.

• Documenting– Code needs to contain documentation that describes to the

reader what the code is doing– Two types of comments are used for documentation

• Internal and external documentation

– Internal documentation is for the programmers to read– External documentation is for the user

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2.3 Coding, Documenting, and Testing

• Testing– Create test data that will be used to check the

program’s correctness. • Use desk checking (or walking through a program by hand

with a set of data that you know the answer to)

– Check that the program will catch errors by using test data designed to create errors

– The more testing of various types of data you can use, the more likely you are to have a program that is free of errors.

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Types of Errors

• Syntax errors: a violation of the programming language’s rules for creating valid statements – May be caused by incorrect grammar or punctuation, or

misspelling a keyword– The program will not run at all with syntax errors

• Logic errors: the program runs, but does not produce the expected results– May be caused by using an incorrect formula, or incorrect

sequence of statements, etc.– Sometimes called runtime errors– These errors can be detected during the desk checking phase of

the programming cycle.

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2.4 Commercial Programs:Testing and Documenting

External documentation

Purposes:

1. Documentation in a user’s guide or on-screen help system provides information about the program for the end users

2. Documentation in a maintenance manual provides information about how the program code accomplishes its purposes

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The User’s Guide

• Usually written during alpha or beta test phases

• Written by a technical writer

• Forms of user’s guides:– Tutorials– Thematic approach– Alphabetical order

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Documentation for other programmers

• Program maintenance manual– For programming experts to help them fix or

enhance code written by other programmers

• Design documentation– Written by programmer to explain rationale

behind methods and code used

• Trade Study documentation– A research tool – An attempt to find the best solution

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2.5 Structured Programming

• A method for designing and coding programs in a systematic, organized manner

• It combines the principles of top-down design, modularity and the use of the three accepted control structures of sequence, repetition and selection

• Sequence, repetition and selection can be expressed in pseudocode, or with flowcharts

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Flowcharts• A tool for programmers to design programs

– Describes the flow of a program module’s execution with diagrams

– Completely different from hierarchy charts– Connected symbols are used to describe sequence,

repetition, and selection structures– Some prefer to use flowcharting to learn how to

express algorithms, and others prefer to use pseudocode

– Many programs are designed with a combination of pseudocode and flowcharts

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Flowchart Symbols

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Control Structures

• Sequence –in sequential order. – The simplest of control structures – start at the beginning and

continue in sequential order.

• Repetition – repeat statements more than once– Also called a loop, it needs a stop condition, i.e, the program will

continue to loop until some condition is met.

• Selection – selectively execute statements– Called a branch, it requires a condition to determine when to

execute statements.

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Flowchart for a Loop

Loop or repetition structure flowchart:

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Flowchart for a Decision

Decision or selection structure flowchart:

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2.6 An Introduction to GUIs and OOP

• GUI – Graphical User Interface– Users interact with software using a mouse, to select

from menu choices, clicking on buttons, etc. – Development of GUI software uses tools specifically

designed for that task.– Event-driven programming is the development of

software where the flow of control is based on the user’s clicking on menus and buttons, etc. These user actions are called events.

• Event-driven programming still uses the basic principles of structured programming – program modules, control structures, good programming style, and program testing.

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Object Oriented Programming

• Focus is on the objects that will be used to solve the problems.

• Object – a structure that contains attributes and methods (data and process)

• Object-oriented design starts with identifying the required objects.

• Java, C++, JavaScript and others are languages based on object-oriented programming

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Importance of Structured Programming

• Structured, event-driven, and object-oriented programming techniques are not separate form each other.

• All require the basic principles of structured programming – program modules, control structures, good programming style, and program testing.

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Style Pointers

• Write modular programs

• Use descriptive variable names

• Provide a welcome message for the user

• Use a prompt before an input

• Identify program output

• Document your programs

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Pseudocode Language (Ch 2)In this chapter we added a way to create and call modules in our programs.

Input AssignmentInput Variable Set Variable = 10

Set Variable = AnotherVariable

Output Arithmetic OperationsWrite “literal text” ( ) ^ * / + -Write VariableWrite “literal text”, Variable

Create a module Call a sub-moduleModuleName Call ModuleName …. End