6804068 chapter 01 background

7/21/2019 6804068 Chapter 01 Background

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Chapter 1

Class 2

CS 101

Chapter 1: Introduction

Aaron Bloomfield

Spring 2007


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Lets begin

Goal

Teach you how to program effectively

Skills and information to be acquired What the heck all this means

Problem solving

Object-oriented design

Java


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So, what is a computer, anyway?


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What is a computer?

Not a rhetorical question!

Adevice that computes

especially a programmable electronic machine thatperforms high-speed mathematical or logicaloperations or that assembles, stores, correlates, or

otherwise processes information From American Heritage Dictionary of the English

Language, 4thEdition


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So what is a computation?

The act or process of computing

Duh!

Definition of computing:

To determine by the use of a computer

To determine by mathematics, especially by numericalmethods: computed the tax due

My revised definition for computing:

The act of taking a problem with specific inputs anddetermining a specific answer (output)


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Axiom

By definition, a (properly functioning) computer willalwaysproduce the same output given the sameinput

So how do we compute random numbers?


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The first computers

Abacusperformed mathematical computations

Primarily thought of as Chinese, but also Japanese, Mayan, Russian,and Roman versions

Can do square roots and cube roots

Scales computed relative weight oftwo items

Computed if the first items weightwas less than, equal to, or greater

than the second itemsweight


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Stonehenge


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Computer Size

ENIAC then

ENIAC today


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Algorithms


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So what do we do with a computer

now that we have one?

We have to tell a computer what to do!

Computers have no intelligence of their own

We tell a computer what to do by writing a

computer program, oralgorithm In this course, welluse Java


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Algorithms

What is an algorithm?

A step-by-step problem-solving procedure,

especially an established, recursive computationalprocedure for solving a problem in a finite numberof steps

From American Heritage Dictionary of the EnglishLanguage, 4thEdition

Weveseen lots of algorithms before


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Example algorithm: map directions


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Example algorithm: car radio removal


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Example algorithm: Recipes


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An optical illusion


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Algorithm correctness


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Incorrect algorithms

Not all algorithms aregood

So then what makes an algorithmbad?

Can be wrong

Can be inefficient

Can never stop

Can have other problems as well


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Incorrect algorithms: just plain wrong

From http://en.for-ua.com/blog/2005/12/09/102028.html
http://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.htmlhttp://en.for-ua.com/blog/2005/12/09/102028.html


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Inefficient algorithms: MapQuest directions

Consider directions to get around grounds


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Note that this is not an incorrect algorithm!

Just a veryinefficient one


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Incorrect algorithms: Shampoo directions


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Incorrect algorithms: Shampoo directions

Lather, rinse, repeat

This algorithm repeats forever! It never halts

Note that humans know to not to spend forever performing thealgorithm

But computers do not! Remember, they have zero intelligence

Hence the overplayed (and not very funny) computer joke: How did the computer scientist die in the shower?

S/he read the directions: lather, rinse, repeat


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Incorrect algorithms: Inexact recipes


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Incorrect algorithms: summation

Consider this algorithm: Given an integer n

Keep track of an ongoing sum (starts at 0)

Repeat Add nto the ongoing sum

Subtract 1 from n

Until nis zero

Whatswrong with this algorithm? Will it ever stop?

Will it alwaysstop? Are you sure?


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Our goal

Is to write correct and efficient algorithms for acomputer to follow

Remember that computers are dumb!

We arentgoing to worry about the efficient part inthis course

But what doescorrectmean?


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Correct algorithms

Consider an algorithm to display the color blue

Is this blue?

Is this blue?

What about this?

And this one?

Definitely

Also, yes: two correct results!

Maybe (could be green)

Definitely not


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Note that this is not an incorrect algorithm!

Just a veryinefficient one


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So what does all this mean?

Humans specify algorithms without a lot of precision

Display the colorblue

Get me fromheretothere

When there isntmuch precision, there are often multiple answers

Computers need more precision Display the color 0x0000ff (royal blue):

There is only one possible outcome

Find the shortest route fromheretothere

We need to be very specific when we specify things to acomputer

Computers are dumb!


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Carved watermelons


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Programming a computer


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How do we tell all this to a computer?

Computer: Tea, Earl Gray, hot

Jean-Luc Picard from Star Trek

Unfortunately, that doesntwork so well today

Computers dontunderstand English


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First Programming Languages

Ada Lovelace (1833)

Programmed of Babbagesanalytical engine

ENIAC (1945)

Programmed by plugging wires

Binary

100100010101001010101010

Assembly FORTRAN (1954)


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Programming Languages

Common programming languages:

BASIC

COBOL

Pascal C (1972) by Dennis Ritchie

C++ (1985) by Bjarne Stroustrup

Java (1991) by James Gosling and others at Sun

Microsystems


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Background


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Computing units of measure

A bit is either a 1 or a 0

On or off, true or false, etc.

A byte is 8 bits:

01001010 As there are 8 bits per byte, each byte can hold 28=256 values

01001010 = 74

All computing measurements are in terms of bytes


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Kilo (K) = 1,000 (thousand)

Mega (M) = 1,000,000 (million)

Giga (G) = 1,000,000,000 (billion)

Tera (T) = 1,000,000,000,000 (trillion) Kilo = 210= 1,024

Mega = (1024)2= 1,048,576

Giga = (1024)3= 1,073,741,824

Tera = (1024)4= 1,099,511,627,776

= Kibi (Ki)

= Mebi (Mi)

= Gibi (Gi)= Tebi (Ti)


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An unformatted text document (such as a Java program)

3 pages per kilobyte (1,000 bytes)

A formatted document (such as a Word file)

About 5k per page with formatting

A digital camera picture About 1 Mb each (1,000,000 bytes)

An MP3 music file

5 Mb for a 5 minute song

A music file on a CD 50 Mb for a 5 minute song

10 times the size of an MP3!

A movie clip

About 10 Mb per minute of (TV-sized) video


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A marketing trick

This hard drive has250,059,350,016bytes

= 250.06 Gigabytes = 232.89 Gibibytes

Guess which one

they use when theyare advertising thedrive?

T d d ti t


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Todays demotivators


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Chapter 1

Class 3

Our first Java program


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Programming Task

DisplayHelloWorld!


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HelloWorld.java

// Purpose: say hello!

public class HelloWorld {

public static void main(String[] args) {

System.out.println (Hello,world!");

}

}One statement makes up the action of method main()Method main() is part of class HelloWorldA method is a named piece of code that performs some action orimplements a behaviorAn application program is required to have a public static voidmethod named main().


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Sample output


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Program parts


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Common Language Elements

There are some concepts that are common tovirtually all programming languages.

Common concepts:

Key words Operators

Punctuation

Programmer-defined identifiers

Strict syntactic rules


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Java Documentation

Familiarize yourself with the Java documentation

It will save you lots of time!

A link to it is on the website

We will go over it in a future lab as well


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Key Words

Key words in the sample program are: public

class

static

void

String String is not really a key word but is the name of a predefined

class in Java

Wellgo over the difference between these later Key words

lower case (Java is a case sensitive language).

cannot be used as a programmer-defined identifier.


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Programming Languages

Some Java key words have no meaning but arereserved to prevent their use. (ex. goto, const,include)

Semi-colons are used to end Java statements;however, not all lines of a Java program end astatement.

Part of learning Java is to learn where to properly

use the punctuation.


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Lines vs Statements

There is a difference between lines and statementswhen discussing source code.

System.out.println(

message);

This is one Java statement written using two lines.Do you see the difference?

A statement is a complete Java instruction thatcauses the computer to perform an action.


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Good commenting

Necessary so others can re-use your code

And so the graders can understand it!

A well commented program:

// Authors: J. P. Cohoon and J. W. Davidson

// Purpose: display a quotation in a console window

public class DisplayForecast {

// method main(): application entry point


System.out.print("I think there is a world market for");

System.out.println(" maybe five computers.");

System.out.println(" Thomas Watson, IBM, 1943.");

}

}


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Bad commenting

// Thomas J. Watson (February 17, 1874 - June 19, 1956) is

// considered to be the founder of IBM. He was one of the

// richest men of his time and called the world's greatest

// salesman when he died.

// Watson was born in Campbell, New York. His formal

// education consisted of only a course in the Elmira

// School of Commerce. His first job was at age 18 as

// a bookkeeper in Clarence Risley's Market in Painted

// Post, New York. Later he sold sewing machines and

// musical instruments before joining the National Cash

// Register Company as a salesman in Buffalo. He eventually

// worked his way up to general sales manager. Bent on

// inspiring the dispirited NCR sales force, Watson

// introduced the motto, "THINK," which later became

// a widely known symbol of IBM.

// Although he is well known for his alleged 1943 statement:

// "I think there is a world market for maybe five computers"

// there is no evidence he ever made it. The author Kevin

// Maney tried to find the origin of the quote. He has been

// unable to locate any speeches or documents of Watson's

// that contain this, nor is it present in any contemporary

// articles about IBM. The earliest known citation is from

// 1986 on Usenet in the signature of a poster from Convex

// Computer Corporation as "I think there is a world market

// for about five computers" --Remark attributed to Thomas

// J. Watson (Chairman of the Board of International

// Business Machines),1943

// While at NCR, he was convicted for illegal anti-

// competitive sales practices (e.g. he used to have

// people sell deliberately faulty cash registers, either

// second-hand NCR or from competitors; soon after the

// second-hand NCR or competitors cash register failed,

// an NCR salesperson would arrive to sell them a brand

// new NCR cash register). He was sentenced, along with

// John H. Patterson (the owner of NCR), to one year of

// imprisonment. Their conviction was unpopular with the

// public, due to the efforts of Patterson and Watson to

// help those affected by the 1913 Dayton, Ohio floods,

// but efforts to have them pardoned by President Woodrow

// Wilson were unsuccessful. However, the Court of

// Appeals overturned the conviction on appeal in 1915,

// on the grounds that important defense evidence should

// have been admitted.

public class DisplayForecast {

// method main(): application entry point


System.out.print("I think there is a world market for");

System.out.println(" maybe five computers.");

System.out.println(" Thomas Watson, IBM, 1943.");

}

}


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More bad commenting

From the context-switching code of Unix V6 (file: slp.c)

/** If the new process paused because it was* swapped out, set the stack level to the last call* to savu(u_ssav). This means that the return* which is executed immediately after the call to aretu

* actually returns from the last routine which did* the savu.** You are not expected to understand this.*/

if(rp->p_flag&SSWAP) {rp->p_flag =& ~SSWAP;aretu(u.u_ssav);

}

Source: http://www.tuhs.org/Archive/PDP-11/Trees/V6/usr/sys/ken/slp.c


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Human stupidity


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Chapter 1

Extra Material

The Programming Process


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1. Clearly define what the program is to do.

2. Visualize the program running on the computer.

3. Use design tools to create a model of the program.

4. Check the model for logical errors.


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5. Enter the code and compile it.

6. Correct any errors found during compilation.Repeat Steps 5 and 6 as many times as necessary.

7. Run the program with test data for input.

8. Correct any runtime errors found while running theprogram.Repeat Steps 5 through 8 as many times as necessary.

9. Validate the results of the program.


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Software Engineering

Encompasses the whole process of crafting computersoftware.

Software engineers perform several tasks in the

development of complex software projects. designing,

writing,

testing,

debugging,

documenting, modifying, and

maintaining.


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Software Engineering

Software engineers develop:

program specifications,

diagrams of screen output,

diagrams representing the program components and theflow of data,

pseudocode,

examples of expected input and desired output.


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Other buzzwords from the chapter

Im not expecting you to fully understand theseafter reading chapter 1

Procedural programming

Object oriented programming Data hiding

Code reusability

Classes vs. objects

Inheritance We will see all of these before the semester ends


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Computer Systems


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Computer Systems

Hardware

The central processing unit (CPU)

Main memory

Secondary storage devices Input and Output devices

Software

Operating systems

Application software


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Computer Systems: Hardware

Input Devices

Output Devices

Input / OutputDevices

ALU

Control Unit

RAM


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Computer Systems: Hardware

Computer hardware components are the physicalpieces of the computer.

The major hardware components of a computer

are: The central processing unit (CPU)

Main memory

Secondary storage devices

Input and Output devices


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Central Processing Unit

Arithmetic

Logic

Unit

ControlUnit

CPU

Instruction (input) Result (output)


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Central Processing Unit

The CPU performs the fetch, decode, execute cyclein order to process program information.

Fetch

The CPUs control unit fetches, from main memory,

the next instruction in the sequence of programinstructions.

Decode

The instruction is encoded in the form of a

number. The control unit decodes the

instruction and generates an electronic signal.

ExecuteThe signal is routed to the appropriate

component of the computer (such as the ALU,

a disk drive, or some other device). The signal

causes the component to perform an

operation.


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Main Memory (aka RAM)

Commonly known as random-access memory

(RAM)

RAM

contains: currently running programs

data used by those programs

is volatile when the computer is turned off, the contents of RAM are

erased.

short-term memory


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Secondary Storage

Secondary storage devices are capable of storinginformation for longer periods of time

non-volatile

long-term memory Examples

Hard drive

CD RW drive

DVD RAM drive Compact Flash card


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Input Devices

Input is any data the computer collects from theoutside world.

That data comes from devices known as input

devices. Common input devices:

Keyboard

Mouse

Scanner

Digital camera

O i


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Output Devices

Output is any data the computer sends to theoutside world.

That data is displayed on devices known as output

devices Common output devices:

Monitors

Printers

Some devices such as disk drives perform inputand output and are called I/O devices(input/output).

C S S f


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Computer Systems: Software

Software refers to the programs that run on acomputer.

Two classifications of software:

Operating Systems Application Software

O ti S t


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Operating Systems

An operating system has two functions: Control the system resources.

Provide the user with a means of interaction with thecomputer.

Operating systems can be either

single tasking (run one program at a time)

DOS

multi-tasking (run many programs at once) Windows

Unix

Apple

O ti S t


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Operating Systems

Operating systems can also be categorized as single user

only one user to operate the computer at a time

Examples:

DOS Windows 95/98/ME

multi-user allow several users to run programs and operate the computer at

once.

Examples Unix

BSD

Windows NT/2000/XP

OS/X

A li ti S ft


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Application Software

Programs that make the computer useful to theuser

Spreadsheets

Word processors Accounting software

Tax software

Games

6804068 chapter 01 background

Documents