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Introduction to Computers, the Internet and the Web

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The chief merit of language is clearness.

Galen

Our life is frittered away by detail. …Simplify, simplify.

Henry David Thoreau

He had a wonderful talent for packing thought close, and rendering it portable.

Thomas B. Macaulay

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Man is still the most extraordinary computer of all.

John F. Kennedy

Things are always at their best in their beginning.

Blaise Pascal.

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OBJECTIVES

In this chapter you will learn:

Basic computer concepts.
The different types of programming languages.
The history of the C programming language.
The purpose of the C Standard Library.
The elements of a typical C program development environment.
Why it is appropriate to learn C in a first programming course.
How C provides a foundation for further study of programming languages in general and of C++, Java and C# in particular.
The history of the Internet and the World Wide Web.

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1.1 Introduction

1.2 What Is a Computer?

1.3 Computer Organization

1.4 Early Operating Systems

1.5 Personal, Distributed and Client/Server Computing

1.6 Machine Languages, Assembly Languages and�High-Level Languages

1.7 Fortran, COBOL, Pascal and Ada

1.8 History of C

1.9 C Standard Library

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1.10 C++

1.11 Java

1.12 BASIC, Visual Basic, Visual C++, Visual C# and .NET

1.13 Key Software Trend: Object Technology

1.14 Typical C Program Development Environment

1.15 Hardware Trends

1.16 History of the Internet

1.17 History of the World Wide Web

1.18 Notes About C and This Book

1.19 Web Resources

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1.1 Introduction

We will learn

The C programming language
Structured programming and proper programming techniques

This book also covers C++

Chapters 18-27 introduce the C++ programming language

This course is appropriate for

Technically oriented people with little or no programming experience
Experienced programmers who want a deep and rigorous treatment of the language

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1.2 What is a Computer?

Computer

Device capable of performing computations and making logical decisions
Computers process data under the control of sets of instructions called computer programs

Hardware

Various devices comprising a computer
Keyboard, screen, mouse, disks, memory, CD-ROM, and processing units

Software

Programs that run on a computer

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1.3 Computer Organization

Six logical units in every computer:

Input unit

Obtains information from input devices (keyboard, mouse)

Output unit

Outputs information (to screen, to printer, to control other devices)

Memory unit

Rapid access, low capacity, stores input information

Arithmetic and logic unit (ALU)

Performs arithmetic calculations and logic decisions

Central processing unit (CPU)

Supervises and coordinates the other sections of the computer

Secondary storage unit

Cheap, long-term, high-capacity storage
Stores inactive programs

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1.4 Early Operating Systems

Batch processing

Do only one job or task at a time

Operating systems

Manage transitions between jobs
Increased throughput

Amount of work computers process

Multitasking

Computer resources are shared by many jobs or tasks

Timesharing

Computer runs a small portion of one user’s job then moves on to service the next user

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1.5 Personal Computing, Distributed Computing, and Client/Server Computing

Personal computers

Economical enough for individual

Distributed computing

Computing distributed over networks

Client/server computing

Sharing of information across computer networks between file servers and clients (personal computers)

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1.6 Machine Languages, Assembly Languages, and High-level Languages

Three types of programming languages

Machine languages

Strings of numbers giving machine specific instructions
Example:

+1300042774

+1400593419

+1200274027

Assembly languages

English-like abbreviations representing elementary computer operations (translated via assemblers)
Example:

LOAD BASEPAY

ADD OVERPAY

STORE GROSSPAY

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1.6 Machine Languages, Assembly Languages, and High-level Languages

Three types of programming languages (continued)

High-level languages

Codes similar to everyday English
Use mathematical notations (translated via compilers)
Example:

grossPay = basePay + overTimePay

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1.7 Fortran, COBOL, Pascal and Ada

Fortran

developed by IBM Corporation in the 1950s
used for scientific and engineering applications that require complex mathematical computations

COBOL

developed in 1959 by computer manufacturers, the government and industrial computer users
used for commercial applications that require precise and efficient manipulation of large amounts of data

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1.7 Fortran, COBOL, Pascal and Ada

Pascal

Developed by Professor Niklaus Wirth in 1971
Designed for teaching structured programming

Ada

Developed under the sponsorship of the U.S. Department of Defense (DOD) during the 1970s and early 1980s
Able to perform multitasking

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1.8 History of C

C

Evolved by Ritchie from two previous programming languages, BCPL and B
Used to develop UNIX
Used to write modern operating systems
Hardware independent (portable)
By late 1970's C had evolved to "Traditional C"

Standardization

Many slight variations of C existed, and were incompatible
Committee formed to create a "unambiguous, machine-independent" definition
Standard created in 1989, updated in 1999

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Portability Tip 1.1

Because C is a hardware-independent, widely available language, applications written in C can run with little or no modifications on a wide range of different computer systems.

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1.9 C Standard Library

C programs consist of pieces/modules called functions

A programmer can create his own functions

Advantage: the programmer knows exactly how it works
Disadvantage: time consuming

Programmers will often use the C library functions

Use these as building blocks

Avoid re-inventing the wheel

If a pre-made function exists, generally best to use it rather than write your own
Library functions carefully written, efficient, and portable

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Performance Tip 1.1

Using Standard C library functions instead�of writing your own comparable versions can improve program performance, because these functions are carefully written to perform efficiently.

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Portability Tip 1.2

Using Standard C library functions instead�of writing your own comparable versions can improve program portability, because these functions are used in virtually all Standard C implementations.

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1.10 C++

C++

Superset of C developed by Bjarne Stroustrup at Bell Labs
"Spruces up" C, and provides object-oriented capabilities
Dominant language in industry and academia

Learning C++

Because C++ includes C, some feel it is best to master C, then learn C++
Starting in Chapter 18, we begin our introduction to C++

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1.11 Java

Java is used to

Create Web pages with dynamic and interactive content
Develop large-scale enterprise applications
Enhance the functionality of Web servers
Provide applications for consumer devices (such as cell phones, pagers and personal digital assistants)

Java How to Program

Closely followed the development of Java by Sun
Teaches first-year programming students the essentials of graphics, images, animation, audio, video, database, networking, multithreading and collaborative computing

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1.12 BASIC, Visual Basic, Visual C++, Visual C# and .NET

BASIC

Developed in the mid-1960s by Professors John Kemeny and Thomas Kurtz of Dartmouth College as a language for writing simple programs

Visual Basic

Introduced by Microsoft in 1991 to simplify the process of making Windows applications

Visual Basic, Visual C++, and Visual C#

Designed for Microsoft’s .NET programming platform

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1.13 Key Software Trend: Object Technology

Objects

Reusable software components that model items in the real world
Meaningful software units

Date objects, time objects, paycheck objects, invoice objects, audio objects, video objects, file objects, record objects, etc.
Any noun can be represented as an object

Very reusable
More understandable, better organized, and easier to maintain than procedural programming
Favor modularity

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1.14 Typical C Program Development Environment

Phases of C Programs:

Edit
Preprocess
Compile
Link
Load
Execute

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Fig. 1.1 | Typical C development environment.

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Common Programming Error 1.1

Errors like division-by-zero occur as a program runs, so these errors are called runtime errors or execution-time errors. Divide-by-zero is generally a fatal error, i.e., an error that causes the program to terminate immediately without successfully performing its job. Nonfatal errors allow programs to run to completion, often producing incorrect results. [Note: On some systems, divide-by-zero is not a fatal error. Please see your system documentation.]

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1.15 Hardware Trends

Every year or two the following approximately double:

Amount of memory in which to execute programs
Amount of secondary storage (such as disk storage)

Used to hold programs and data over the longer term

Processor speeds

The speeds at which computers execute their programs

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1.16 History of the Internet

The Internet enables

Quick and easy communication via e-mail
International networking of computers

Packet switching

The transfer of digital data via small packets
Allows multiple users to send and receive data simultaneously

No centralized control

If one part of the Internet fails, other parts can still operate

TCP/IP
Bandwidth

Information carrying capacity of communications lines

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1.17 History of the World Wide Web

World Wide Web

Locate and view multimedia-based documents on almost any subject
Makes information instantly and conveniently accessible worldwide
Possible for individuals and small businesses to get worldwide exposure
Changing the way business is done

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1.18 General Notes About C�and This Book

Program clarity

Programs that are convoluted are difficult to read, understand, and modify

C is a portable language

Programs can run on many different computers
However, portability is an elusive goal

We will do a careful walkthrough of C

Some details and subtleties are not covered
If you need additional technical details

Read the C standard document
Read the book by Kernigan and Ritchie

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Good Programming Practice 1.1

Write your C programs in a simple and straightforward manner. This is sometimes referred to as KIS (“keep it simple”). Do not “stretch” the language by trying bizarre usages.

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Portability Tip 1.3

Although it is possible to write portable programs, there are many problems between different C compilers and different computers that make portability difficult to achieve. Simply writing programs in C does not guarantee portability. The progammer will often need to deal directly with complex computer variations.

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Software Engineering Observation 1.1

Read the manuals for the version of C you are using. Reference these manuals frequently to be sure you are aware of the rich collection of C features and that you are using these features correctly.

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Software Engineering Observation 1.2

Your computer and compiler are good teachers. If you are not sure how a feature of C works, write a sample program with that feature, compile and run the program and see what happens.

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