SE491: Software Construction A 1

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An Object-Oriented Approach to Programming Logic and Design
Fourth Edition

Chapter 1

An Overview of Computer Programming

Objectives

In this chapter, you will learn about:

Computer components and operations
Simple program logic
The evolution of programming models
The steps in the programming process
Pseudocode and flowcharts
Program comments
Programming and user environments

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations

Computer system
Combination of all components required to process and store data using a computer
Two major computer system components
Hardware
Physical devices associated with the computer
Software
Computer instructions that tell the hardware what to do
Programs (sets of instructions) written by programmers
Application software: programs applied to a task
System software: programs that manage computer resources

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations (cont’d)

Three major hardware and software operations
Input
Processing
Output
Input operation
A means for data to enter a computer through an input device such as a mouse or keyboard

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations (cont’d)

Processing data operation
Organizing or sorting data
Checking for accuracy
Performing mathematical operations
Tasks occur in central processing unit (CPU)
Output operation
Means to view, print, or store data using output devices
Printer or monitor
Storage devices (e.g., disks, flash media)
Information: data that has been processed

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations (cont’d)

Programming language
Instructions controlling data manipulation
Examples include Visual Basic, C#, C++, or Java
Syntax
Rules governing word usage and punctuation for a programming language
Syntax errors: mistakes in a language’s usage
Program code
Instructions written in a programming language

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations (cont’d)

Computer memory (RAM)
Temporary, internal storage
Executable statements
Statements that carry out a program’s actions
Compiler or interpreter
Translate high level programming language statements into low-level machine or binary language
Point out syntax errors

An Object-Oriented Approach to Programming Logic and Design

Understanding Computer Components and Operations (cont’d)

Compiler
Translates entire program before execution
Interpreter
Translates an instruction just prior to execution
Source code
Program statements written in a programming language
Object code
Code translated into machine language statements

An Object-Oriented Approach to Programming Logic and Design

Understanding Simple Program Logic

Logic errors
Program may execute but produces incorrect results
Can be avoided by
Writing program instructions in specific sequence
Removing extraneous instructions
Including all required instructions
Example of logic errors in cake-making instructions

Stir

Add two eggs

Add a gallon of gasoline

Bake at 350 degrees for 45 minutes

Add three cups of flour

An Object-Oriented Approach to Programming Logic and Design

Danger:
Do not follow these cake-baking instructions!

An Object-Oriented Approach to Programming Logic and Design

Understanding Simple Program Logic (cont’d)

Computer programs include steps that perform input, processing, and output
Sample instructions written in English-like language
Program doubles any given number
Requires three operations: input, processing, and output

input myNumber  input

myAnswer = myNumber * 2  processing

output myAnswer  output

An Object-Oriented Approach to Programming Logic and Design

Understanding the Evolution
of Programming Models

Modern computer programs
Around since 1940s
Oldest programming languages
Programmers worked with memory addresses
Memorized awkward codes associated with machine languages
Written as one piece

An Object-Oriented Approach to Programming Logic and Design

Understanding the Evolution
of Programming Models (cont’d)

Newer programming languages
Look like natural language
Use meaningful names for memory locations
Allow creation of self-contained modules or program segments
Can be pieced together
Can be reused

An Object-Oriented Approach to Programming Logic and Design

Understanding the Evolution
of Programming Models (cont’d)

Major program development techniques
Procedural programming
Focuses on actions that are carried out
Breaks down processes into manageable subtasks
Object-oriented programming – focuses on objects
Objects: entities that have attributes, behaviors, and states
Attributes: object features
Behaviors: what object does
States: set of all values of attributes
Primary difference is focused on early planning stages

An Object-Oriented Approach to Programming Logic and Design

Understanding the Evolution
of Programming Models (cont’d)

Object-oriented approach
Defining the objects needed to accomplish a task
Each object maintains its own data and carries out tasks
“Natural” way of thinking about the world
Types of object-oriented approach applications
Computer simulations
Mimic real-world activities
Users apply programs to tasks after the programs are written
Graphical user interfaces (GUIs)
Users interact with program in graphical environment

An Object-Oriented Approach to Programming Logic and Design

Understanding the Steps
in the Programming Process

System program
A group of many programs
Object-oriented approach involves
Analyzing the system
Designing the system
Writing the programs
Programmer may do all tasks or use systems analysts and/or software testers

An Object-Oriented Approach to Programming Logic and Design

Understanding the Steps
in the Programming Process (cont’d)

Types of software testing
Black box
Tester provides input and checks for valid output
White box
Tester looks at code, tests all logical paths

An Object-Oriented Approach to Programming Logic and Design

Analyzing the Program or System

Programmers provide a service to users
Object-oriented analysis (OOA)
Understand the users’ needs
Needs are often not well defined
Can be difficult and time consuming
Frequently, several program revisions are necessary to satisfy the user

An Object-Oriented Approach to Programming Logic and Design

Designing the System

Designers using object-oriented design (OOD)
Envision the objects needed
Determine objects’ attributes and behaviors
Decide the relationship between objects
Describe how objects communicate with and react to each other
Expressed as verb phrases
Examples of relationships: “Has a,” “is a,” “creates a”
Class
A general category that describes entities
May be reused from other programs or modified

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs

Writing a program involves several subtasks
Developing the program logic
Coding the program
Translating the program into machine language
Testing the program

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Planning the logic
Heart of the programming process
Also referred to as developing an algorithm
Decide steps to include and their order
Planning tools
Flowcharts and pseudocode
Both use English-like code
Language syntax not a concern
Desk-checking
Reviewing program logic on paper

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Coding the program
Writing program statements in a programming language
Object-oriented languages
C++, C#, Java, Visual Basic, SmallTalk, OO COBOL, and Simula
Create objects and establish communication between them
Language chosen determines syntax
Coding usually less difficult than planning step

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Use software to translate program into machine language
Many programming languages
Computer knows only machine language (1s and 0s)
Compilers or interpreters
Translate English-like, high-level programming language into low-level machine language

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Syntax error
Occurs when translator cannot translate the code
Causes: misspellings, illegal grammar, non-existent words
Programmer must correct code and recompile the program before it can execute

An Object-Oriented Approach to Programming Logic and Design

Creating an executable program

Figure 1-1

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Testing the program
Program that is free of syntax errors is not necessarily free of logical errors
Must test for logical errors
May require entering of sample data
Select test data carefully
Error discovery may require changes to program logic

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

After the program is written and tested
Ready to be used
Additional tasks associated with programs written for organizations
Preparing manuals
Training users
Converting existing data to new system’s format
Conversion
Actions an organization take to switch to a new program
Can take months or years to accomplish

An Object-Oriented Approach to Programming Logic and Design

Writing and Testing Programs (cont’d)

Maintenance
Process of making required changes after program is put into production
Reasons why maintenance may be necessary
Fixing previously undiscovered errors
Updating values such as a tax rate
Changing format of input data
Input data may no longer be available
User wants additional functionality

An Object-Oriented Approach to Programming Logic and Design

Using Pseudocode and Flowcharts

Pseudocode
English-like representation of logical program steps
Looks like programming language but is not
Flexible planning tool
Example

Starting and ending statements often used
Punctuation and syntax are not important

An Object-Oriented Approach to Programming Logic and Design

start

input myNumber

myAnswer = myNumber * 2

output myAnswer

stop

An Object-Oriented Approach to Programming Logic and Design

Drawing Flowcharts

Flowchart
Pictorial representation of logical program steps
Helps programmer visualize how statements connect
Uses geometric shapes connected with arrows (flowlines)
Common flowchart symbols
Input symbols (parallelograms)
Processing symbols (rectangles)
Output symbols (parallelograms)
Terminal symbols (lozenges – flattened ovals)
Decision symbols (diamonds)

An Object-Oriented Approach to Programming Logic and Design

Drawing Flowcharts (cont’d)

An Object-Oriented Approach to Programming Logic and Design

Flowchart and pseudocode of a program that doubles a number if it is less than 10

Figure 1-3

An Object-Oriented Approach to Programming Logic and Design

Drawing Flowcharts (cont’d)

Software applications with flowcharting tools
Microsoft Word
Microsoft PowerPoint
Visio
Visual Logic

An Object-Oriented Approach to Programming Logic and Design

Understanding Program Comments

Program comments
Non-executing statements in a program added for documentation
Programmers write comments for themselves and others who read program
Minimally, comments should include author, date, and purpose of the program
C++, Java, and C# use two forward slashes

// This is a comment

An Object-Oriented Approach to Programming Logic and Design

Annotation symbol used for comments on a flowchart

An Object-Oriented Approach to Programming Logic and Design

Three-sided box with dashed line connects to the step it explains

Figure 1-4

An Object-Oriented Approach to Programming Logic and Design

Understanding Programming
and User Environments

Flowcharts created by hand or with software
Pseudocode written by hand or with a word processor
Plain text editor
Text editor in an integrated development environment (IDE)
Text editor
Program used to create simple text files
Similar to a word processor, but less robust
Example: Notepad in Microsoft Windows
Complete program does not require much disk space

An Object-Oriented Approach to Programming Logic and Design

Understanding Programming and User Environments (cont’d)

Integrated development environment (IDE)
Software package that includes an editor, compiler, and other programming tools
Advantages of using IDE
Uses colors to display various language components
Highlights syntax errors visually
Employs automatic statement completion
Provides tools to step through a program to find errors
Disadvantages of using IDE
Requires much more storage space than plain text editor

An Object-Oriented Approach to Programming Logic and Design

A user might execute program in different environments: command line, GUI
The logical process is the same regardless of the environment

Understanding User Environments

An Object-Oriented Approach to Programming Logic and Design

Executing a number-doubling program in a command-line environment

Executing a number-doubling program in a GUI environment

Figure 1-7

Figure 1-8

An Object-Oriented Approach to Programming Logic and Design

Summary

Hardware and software accomplish three major operations: input, processing, and output
For a program to work properly, you must develop correct logic
Logical errors are more difficult to locate than syntax errors
Developing a system involves analyzing the system, designing it, and writing the programs
Writing programs involves logic planning, coding the program, translating into machine language, and testing

An Object-Oriented Approach to Programming Logic and Design

Summary (cont’d)

Flowcharts and pseudocode are tools for planning a program’s logic
Pseudocode is an English-like representation of a program’s logical steps
Flowchart is a pictorial representation of a program
Program comments document a program
Plain text editor or an integrated development environment (IDE) can be used to type a program
A program’s data input can be at a command line or a graphical user interface (GUI)

An Object-Oriented Approach to Programming Logic and Design