Chapter 4 Computer Languages, Algorithms and Program Development Berlin Chen 2003 Textbooks: 1. Kurt...

Chapter 4

Computer Languages, Algorithms and Program Development

Berlin Chen 2003

Textbooks: 1. Kurt F. Lauckner and Mildred D. Lintner, "The Computer Continuum," Prentice Hall, Second Edition, 2001.

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How do computers know what

we want them to do?

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Outline

• What makes up a language and how do we use language to communicate with each other and with computers?

• How did computer programming languages evolve?• How do computers understand what we are telling

them to do?• What are the steps involved in building a program?• How can we create something that would be visible

on the WWW?

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What is Software

• Software is a set of electronic instructions that tells the computer how to do certain tasks. A set of instructions is often called a program

• When a computer is using a particular program, it is said to be running or executing the program

• The two most common types of programs are system software and application software

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What is Software

Written by different Computer Languages

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What is Software

• System Software– System software exists primarily for the computer

itself, to help the computer perform specific functions

– One major type of system software is the operating system (OS). All computers require an operating system

– The OS tells the computer how to interact with the user and its own devices

– Common operating systems include Windows, the Macintosh OS, OS/2, and UNIX

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What is Software

• Application Software– Application software tells the computer how to

accomplish tasks the user requires, such as creating a document or editing a graphic image.

– Some important kinds of application software are:

Word processing programs Spreadsheet softwareDatabase management Presentation programsGraphics programs Networking software Web design tools and browsers Internet applicationsCommunications programs UtilitiesEntertainment and education Multimedia authoring

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Communicating with People

• Communication cycle

– One complete unit of communication• An idea to be sent (plan how to say)• An encoder (figure out how to phrase it clearly)• A sender (say it)• A medium (through air)• A receiver (with ears)• A decoder (in the brain)• A response

Speaker encodes information

Listener decodes information

Listener returnsfeedback to speaker

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Communicating with People

Message Formulation Message Comprehension

Language System Language System

Neuromuscular Mapping Neural Transduction

Vocal Tract System Cochlea Motion

Speech AnalysisSpeech Generation

Articulatory Parameter

Feature Extraction

Phone, Word, Prosody

Application Semantics,

Actions

Speech Generation Speech Understanding

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Communicating with a Computer

• Substituting a computer for one of the people in the communication process– Process is basically

the same• Response may be

printouts or symbols on the monitor

User encodes information Computer decodes

information

Computerreturns results

to user

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• Between two people:– The person can’t hear you– The phone connection is

broken in mid-call– One person speaks only

French, while the other only Japanese

• Between a person and a computer:– The power was suddenly

interrupted– An internal wire became

disconnected– A keyboard malfunctioned

Communication process is prone to failure: A breakdown can occur any place along the cycle...

When communicating instructions to a computer, areasof difficulty are often part of the encoding and decodingprocess.

Computer hardware is susceptible to failure

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How can we transcribe our human thoughts, usually expressed as words into computer “thoughts”, usually expressed as binary numbers.

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• Programming languages bridge the gap between human thought processes and computer binary circuitry– Communicates data manipulation instructions, such

as read, add, store, print– Programming language: A series of specifically

defined commands designed by human programmers to give directions to digital computers

• Commands are written as sets of instructions, called programs

• All programming language instructions must be expressed in binary code before the computer can perform them

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The Role of Languagesin Communication

• Three fundamental elements of language that contribute to the success or failure of the communication cycle:– Semantics– Syntax– Participants

語意語法參與者

Many subtle differences can be seen when compare programming

languages with human languages

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• Human language:– Refers to the meaning of

what is being said– Words often pick up

multiple meanings.– Phrases sometimes have

idiomatic meanings, e.g.:• Let sleeping dogs lie• Catch the green line and

visit the MFA

• Computer language:– Refers to the specific

command you wish the computer to perform

• Imperative !• Input, Output, Print• Each command has a very

specific meaning.• Computers associate one

meaning with one computer command

– E.g. “SUB” in COBOL

• Semantics: Refers to meaning.

Give a language it’s meaning by associating each language unit “word” with a particular

object or experience, e.g., “tree”

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• Semantics (cont.)– Computer can associate only one meaning with one

computer command– Whereas people can evaluate context (上下前後文 )

to determine which of several meaning a particular word has

– Computers know not thing about context• Each command must has a specific meaning

regardless of context• Computers can’t associate idiomatic meanings with

expressions

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• Human language:– Refers to rules governing

grammatical structure• Pluralization, tense,

agreement of subject and verb, pronunciation, and gender

– Humans tolerate the use of language

• How many ways can you say no? Do they have the same meaning?

• Computer language:– Refers to rules

governing exact spelling and punctuation, plus:

• Formatting, repetition, subdivision of tasks, identification of variables, definition of memory spaces

– Computers do not tolerate syntax errors

• Syntax: Refers to form, or structure

Rule governing exacting spelling and punctuation exist in both.

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• Human language:– In the communication cycle,

humans can respond in more than one way

• Body language/Gestures• Facial expressions• Laughter• human speech

• Computer language:– Computer never uses

anything but binary code - “0”, “1”

– People use programming languages

– Programs must be translated into binary code

– Computers respond by performing the task or not!

• Participants: – Human languages are used by people to communicate with each other. – Programming languages are used by people to communicate with machines.

A successful communication only lies on you !

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• Participants (cont.)– Human communications

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The Programming Language Continuum

• In the Beginning...Early computers consisted of special-purpose computing hardware.– Each computer was designed to perform a particular

arithmetic task or set of tasks– Skilled engineers had to manipulate parts of the

computer’s hardware directly• Some computers required “fat-fingering”.

– Fat-fingering: Engineer needed to position electrical relay switches manually (in either off or on position)

• Others required programs to be hardwired– Hardwiring: Using solder to create circuit boards with

connections needed to perform a specific task

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Invented by Leibniz, 1674

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• ENIAC– Used programs to complete

a number of different mathematical tasks

• Programs were entered by plugging connector cables directly into sockets on a plug-in board

– Set-up could take hours– A program would

generally be used for weeks at a time

– Intricate and error-proneInvented by U. Penn. , 1944

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• In the beginning… To use a computer, you needed to know how to program it

• Today… People no longer need to know how to program in order to use the computer

• To see how this was accomplished, lets investigate how programming languages evolved– First Generation - Machine Language (code)– Second Generation - Assembly Language– Third Generation - People-Oriented Programming Languages– Fourth Generation - Non-Procedural Languages– Fifth Generation - Natural Languages

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• First Generation - Machine Language (code)– Machine language programs were made up of

instructions written in binary code • This is the “native” language of the computer.• Each instruction had two parts: Operation code, Operand

– Operation code (Opcode): The command part of a computer instruction

» Specifies the action to be carried out– Operand (運算元 ): The address of a specific location in

the computer’s memory.• Hardware dependent: Could be performed by only one type

of computer with a particular CPU (a low-level language)

– Unintelligent (difficult to decipher) and error-prone

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• First Generation - Machine Language (code)

Table 4.3.1

Low-level or hardware-dependent languages: computer languages that could be performed by only one type of computer with a particular CPU

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• Second Generation - Assembly Language– Assembly language programs are made up of

instructions written in mnemonics

READ num1READ num2LOAD num1ADD num2STORE sumPRINT sumSTOP

Mnemonic Opcode

Symbolic Operands

– Mnemonics: Uses convenient alphabetic abbreviations to represent operation codes, and abstract symbols to represent operands.

– Each instruction had two parts: Operation code, Operand

– Hardware dependent– Because programs are not written in 1s and 0s,

the computer must first translate the program before it can be executed

• Intelligent and less error-prone

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• Third Generation - People-Oriented Programs– Instructions in these languages are called

statements – High-level languages: Use statements that

resemble English phrases combined with mathematical terms needed to express the problem or task being programmed

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• Third Generation - People-Oriented Programs– Transportable: NOT-Hardware dependent.

• The syntax and semantics of such statements do not reflect the internal machine code or instruction set of any particular computer

– Because programs are not written in 1s and 0s, the computer must first translate the program (using a compiler (編譯器 ) or interpreter (直譯器 ) ) before it can be executed.

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• Third Generation - People-Oriented Programs– Pascal Example: Read in two numbers, add them, and print them

out.

Program sum2(input,output);var num1,num2,sum : integer;

begin read(num1,num2); sum:=num1+num2; writeln(sum)end.

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• Fourth Generation - Non-Procedural Languages– Programming-like systems aimed at simplifying the

programmers task of imparting instructions to a computer

– Many are associated with specific application packages (套裝軟體 )

• Query Languages:• Report Writers• Application Generators

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• Fourth Generation - Non-Procedural Languages– Query Languages

• Enables a person to specify exactly what information they require from the database

• Usually embedded within database management programs

– Report Writers • Takes information retrieved from databases and formats into

attractive, usable output

– Application Generators

• A person can specify a problem, and describe the desired results

• Included with many micro-computer programs (macros)

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• Fourth Generation - Non-Procedural Languages – Object-Oriented Languages

• A language that expresses a computer problem as a series of objects a system contains, the behaviors of those objects, and how the objects interact with each other

• Object: Any entity contained within a system– Examples:

» A window on your screen» A list of names you wish to organize» An entity that is made up of individual parts

• Some popular examples: C++, Java, etc

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• Fourth Generation - Non-Procedural Languages– More about “objects” in programming languages

• You can think an object as a black box, like a VCR with some buttons and lights on it surface

• To use the VCR, you must know what the buttons do– Buttons for the function while lights for the status

• The inside construction of the object is irrelevant when you are using it

– You don’t need to know what the wiring is like inside a VCR to use one

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• Fifth Generation - Natural Languages– Natural-Language: Languages that use ordinary

conversation in one’s own language• Research and experimentation toward this goal

is being done• Intelligent compilers are now being developed to

translate natural language (spoken) programs into structured machine-coded instructions that can be executed by computers

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• Fifth Generation - Natural Languages– So far, we are a long way from speaking any but the

most trivial programs directly into the computer– Effortless, error-free natural language programs are

still some distance into the future

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Assembled, Compiled, or Interpreted Languages

• Except for those written in machine code, all programs must be translated (to the computer’s native language in machine code) before their instructions can be executed

• Computer languages can be grouped according to which translation process is used to convert the instructions into binary code– Assemblers– Interpreters– Compilers

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• Assembled languages– Assembler (組譯器 ): a program used to translate

assembly language programs– Produces one line of binary code per original

program statement• The entire program is assembled before the

program is sent to the computer for execution

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• Interpreted Languages– Interpreter (直譯器 ): A program used to translate

high-level programs– Translates one line of the program into binary code

(several lines of object codes) at a time:• An instruction is fetched from the original source code.• The Interpreter checks the single instruction for errors. (If an

error is found, translation and execution ceases. Otherwise…)• The instruction is translated into binary code.• The binary coded instruction is executed (then discarded).• The fetch and execute process repeats for the entire program.

The program must be reinterpreted each and every time it’s run. It’s a slow process but helpful for locating errors

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• Compiled languages:– Compiler (編譯器 ): a program used to translate high-

level programs– Reads and translates the entire program into binary

code before anything is sent to the CPU for execution• The translation process for a compiled program:

– First, the Compiler checks the entire program for syntax errors in the original source code.

– Next, it translates all of the instructions into binary code.» Produces several lines of object code for each

statement» Two versions of the same program exist: the original

source code version, and the binary code version (object code).

– Last, the CPU attempts execution only after the programmer requests that the program be executed.

A global optimization cab be achieved

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Programming for Everyone

• Several ways to control what your computer does or the way it accomplishes a particular task– Using Macros (巨集 )– Using HTML (HyperText Markup Language): to create

Web Pages– Using Scripts (描述語言、腳本 )

• Each allows customization of current applications

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• Using Macros– Macro: Set of operations within the computer

application that have been recorded for later execution• Once recorded, the macro can be used repeatedly

on any document within that application.• In spreadsheet programs and word processors,

macros are commonly used to speed up repetitive tasks.

– Example: SIG can be stored as a macro that includes a signature message at the end of a document/letters James R. Emmelsohn

Director of Public Relations,Martin Electronics, Detroit Division

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• Using HTML to create Web Pages– HTML: A computer language consisting of special

codes intended to design the layout (or markup) of a Web page. HTML is a formatting language

• Web browsers interpret the HTML code and display the resulting Web pages

• Web browser: A program that displays information from the WWW

• HTML is formatted by tags– The tag language specifies the design and layout of Web

pages– Each tag is delineated by angle brackets before and after

to set the tag apart as complete

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<HTML>

<HEAD>

<TITLE> Title of Web Page </TITLE>

</HEAD>

<BODY bgcolor=#ffffff text=#000000 >

<BODY>

<H1>

<CENTER> Sample Web Page

</CENTER> </H1>

<HR>

<A HREF=“http://www.dogpile.com”> dogpile search engine </A>

</BODY>

</HTML>

• Designates an HTML document

• Beginning of Header section

• Contents of Title bar

• End of Header section

• Background=white, text=black

• Top of the body of the document

• H1=largest text size, H6 is smallest

• CENTER turns on centering

• Turns off centering and large text

• Displays a horizontal rule: thin line

• Links to the dogpile search engine

• </BODY> and </HTML>designate the bottom of the document

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• Scripting– A means by which programmers add extensions or

additional capabilities to an application.

– A series of commands, written to accomplish some task

• Very similar to the concept of a program.• Extends the capabilities of the application where it

is being used.• Examples of scripting languages:

– Perl, C++, VBScript, JavaScript– JavaScript: A scripting language that allows the Web

page designer to add functional features to a formatted web page created in HTML.

» JavaScript is not derived from Java, is only related to Java in name only

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Building a Program

• Whatever type of problem needs to be solved, a careful thought out plan of attack, called an algorithm, is needed before a computer solution can be determined– Mathematical problems, accessing information– Analyze problems and devise plans for their solutions

• Building a program requires for major steps1) Developing the algorithm

2) Writing the program

3) Documenting the program

4) Testing and debugging the program

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Building a Program

• 1) Developing the algorithm– Algorithm: A detailed description of the exact

methods used for solving a particular problem.

– To develop the algorithm, the programmer must first analyze which data users need by asking

• What data has to be fed into the computer?• What information do I want to get out of the computer?

– Logic: Planning the processing of the program. It contains the instructions (or processing part) that cause the input data to be turned into the desired output data

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Building a Program

• The word “algorithm” is derived from the name of the Persian mathematician Mohammed al-Kowậrisimi, who lived during the ninth century and who is credited with developing the step-by-step rules for the addition, subtraction, multiplication, and division of ordinary decimal numbers. When his name was written in Latin it became Algorismus, from which algorithm is derived

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Building a Program

• A step-by-step program plan is created during the planning stage.

• The three major notations for planning detailed algorithms are used by programmers– Flowchart: Series of visual symbols representing the

logical flow of a program

– Pseudocode: A verbal shorthand method that closely resembles a programming language, but does not have to follow a rigid syntax structure

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Building a Program

• A example program “lass-list”

The diamond sharp for

a decision statement

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Building a Program

• 2) Writing the Program– If analysis and planning have been thoroughly done,

translating the plan into a programming language should be a quick and easy task.

• 3) Documenting the Program– During both the algorithm development and program

writing stages, explanations called documentation are added to the code.

• Helps users as well as programmers understand the exact processes to be performed.

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Building a Program

• A example program “lass-list” (cont.)

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Building a Program

• 4) Testing and Debugging the Program– The program must be free of syntax errors.– The program must be free of logic errors (semantic

errors). – The program must be reliable. (produces correct

results)– The program must be robust. (able to detect

execution errors)

Logic errors are more difficult to detect than syntax errors and are harder to correct.

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Building a Program

• Testing and Debugging the Program– Alpha testing: Testing within the company.– Beta testing: Testing under a wider set of conditions

using “sophisticated” users from outside the company.

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Software Development:A Broader View

Type of program Number of LinesThe compiler for a language with a limited instruction set. Tens of thousands of lines

A full-featured word processor. Hundreds of thousands of lines

A microcomputer operating system. Approximately 2,000,000 linesA military weapon management program. (controlling missiles, for example) Several million lines

Measures of effort spent on real-life programs: • Comparing programs by size

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Software Development:A Broader View

– Commercial software is seldom written by individuals• Person-months - equivalent to one person

working 40 hours (eight hours per workday) a week for four weeks.

• Person-years - equivalent to one person working for twelve months.

• Team of 5 people working for 8 weeks = ten person-months.

5*40*8/(40*4)=10

Measures of effort spent on real-life programs: • Comparing programs by time

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Web Page Design Software:Dreamweaver

• What is Web page design software?– The programs that help create pages and their

associated HTML– Dreamweaver: A visual Web page editor primarily for

use by Web design professionals• Created by Macromedia

• Why is it needed?– Allows creation of Web pages without

knowledge of HTML • Without the pain of programming. It’s clumsy to design pages

in HTMLs• Concentrate on the creative aspects of Web page design

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• What minimal functions must the programs for creating Web pages have?– WYSIWIG: “What you see is what you get.”

• Web page designers see exactly what it will look like.

– Allows selection of color scheme (Background and text)

– Allows text manipulation (Typing text where you want it, changing the size, color or style)

– Allows importation and layout of images

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• What types of support are available to enhance its use?– Applets extend the capabilities of HTML

• Applet: A short application program, usually written in Java, which adds enhancement and/or functionality to a Web page.

• Is special support hardware available?– Creating audio/visual materials for the WWW

• Photo digitizers or scanners, video digitizer, and audio digitizer.

• Once these are in a standard digital format, they can be imported to Web development programs.

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• One final note– Dreamweaver and other Web page design software

create Web pages. You still need a place to keep your Web page

• ISP (Internet Service Provider): A company or organization that is used as an access point to the WWW

– The ISP will put your Web page on its server.– You will be given an address where you or others can

access your Web page.

– XML (Extensible Markup Language): for more complex data and processes of Web pages

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Chapter Summary

• Communicating with a Computer– Binary circuitry in computer vs. symbolic thought

processes of the human mind– Programming devised to bridge the gap between the

user and the computer

• The Role of Languages in Communication– Major difference between human languages and

computer languages: semantics, syntax, participants– The syntax of computer instructions are expressed in

narrowly defined patterns

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Chapter Summary

• The Program Language Continuum1.Hardware-wired programs2.Human program a computer but require a program

translation before the computer can perform a task3.Speaking instructions directly into the computer

• Assembled, Complied, or Interpreted Languages– Assemblers translate programs written in assembly

(low-level) language into binary (machine) codes– Interpreters translate and execute one instruction (of

high level language) at a time– Compilers translate an entire program of high level

language) before execution

Chapter 4 Computer Languages, Algorithms and Program Development Berlin Chen 2003 Textbooks: 1. Kurt...

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