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

.

How do computers know what we want them to do?

2

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?

3

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 4

What is Software

Written by different Computer Languages

5

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 6

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:

W

ord processing programs

D

atabase management

G

raphics programs

W

eb design tools and browsers

C

ommunications programs

E

ntertainment and education

S

preadsheet software

P

resentation programs

N

etworking software

I

nternet applications

U

tilities

M

ultimedia authoring 7

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) Speaker encodes information Listener decodes information • A receiver (with ears) • A decoder (in the brain) • A response Listener returns feedback to speaker 8

Communicating with People

Speech Generation Speech Understanding

Message Formulation Language System Neuromuscular Mapping Vocal Tract System

Application Semantics,

Message Comprehension

Actions Phone, Word, Prosody

Language System

Feature Extraction Articulatory Parameter

Neural Transduction Cochlea Motion

Speech Analysis Speech Generation

9

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 returns results to user Computer decodes information 10

Communicating with a Computer

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

• Between two people: • Between a person – The person can’t hear you – The phone connection is broken in mid-call – One person speaks only French, while the other only Japanese and a computer : – The power was suddenly interrupted – An internal wire became disconnected – A keyboard malfunctioned Computer hardware is susceptible to failure When communicating instructions to a computer, areas of difficulty are often part of the encoding and decoding process.

11

Communicating with a Computer

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

12

Communicating with a Computer

•

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 13

The Role of Languages in 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 14

The Role of Languages in Communication •

Semantics

: Refers to

meaning

.

• 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: Give a language it’s meaning by associating each language unit “word” with a particular object or experience, e.g., “tree” – 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 15

The Role of Languages in Communication •

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 16

The Role of Languages in Communication •

Syntax

: Refers to form, or structure

• Human language:

• Computer language:

– Refers to rules governing grammatical structure • Pluralization, tense, agreement of subject and verb, pronunciation, and gender – Refers to rules governing exact spelling and punctuation, plus: – Humans tolerate the use of language • How many ways can you say no? Do they have the same meaning?

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

Computers do not tolerate syntax errors

Rule governing exacting spelling and punctuation exist in both.

17

•

The Role of Languages in Communication

Participants

: – Human languages are used by people to communicate with each other. – Programming languages are used by people to communicate with machines. • Human language: – In the communication cycle, humans can respond in more than one way • Body language/Gestures • Facial expressions • Laughter • human speech A successful communication only lies on you !

• 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!

18

The Role of Languages in Communication

•

Participants

(cont.) – Human communications 19

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 20

The Programming Language Continuum

Invented by Leibniz, 1674 21

The Programming Language Continuum

• 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-prone Invented by U. Penn. , 1944 22

The Programming Language Continuum

• 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 23

The Programming Language Continuum

• 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

computer instruction ): The command part of a » 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

24

The Programming Language Continuum

• First Generation - Machine Language (code)

Low-level or hardware-dependent languages:

computer languages that could be performed by only one type of computer with a particular CPU Table 4.3.1

25

The Programming Language Continuum

• Second Generation - Assembly Language –

Assembly language

programs are made up of instructions written in mnemonics READ READ num1 num2 LOAD STOP num1 ADD STORE sum PRINT num2 sum 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 26

The Programming Language Continuum

• 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 27

The Programming Language Continuum

• 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.

28

The Programming Language Continuum

• 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.

29

The Programming Language Continuum

• 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 30

The Programming Language Continuum

• 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) 31

The Programming Language Continuum

• 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 32

The Programming Language Continuum

• 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 33

The Programming Language Continuum

• 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 34

The Programming Language Continuum

• 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 35

The Programming Language Continuum

36

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 37

Assembled, Compiled, or Interpreted Languages

•

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 38

Assembled, Compiled, or Interpreted Languages

•

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 39

Assembled, Compiled, or Interpreted Languages

•

Compiled languages

: –

Compiler (

編譯器

):

level programs a program used to translate high – 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

.

A global – 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 optimization (

object code

).

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

40

Assembled, Compiled, or Interpreted Languages

41

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 42

Programming for Everyone

•

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,

Programming for Everyone

•

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 44

Programming for Everyone

45

Programming for Everyone

< HTML>

Sample Web Page

---

dogpile search engine • • • • • • • • • • • • 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 and designate the bottom of the document 46

Programming for Everyone

•

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 47

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 steps 1 ) Developing the algorithm 2) Writing the program 3) Documenting the program 4) Testing and debugging the program 48

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 49

Building a Program

• The word “algorithm” is derived from the name of the Persian mathematician Mohammed al Kow ậrisimi, 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 50

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 51

Building a Program

• A example program “lass-list” The diamond sharp for a decision statement 52

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.

53

Building a Program

• A example program “lass-list” (cont.) 54

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 execution errors)

robust

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

55

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.

56

Software Development: A Broader View

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

Type of program

The compiler for a language with a limited instruction set.

A full-featured word processor.

lines

Number of Lines

Tens of thousands of lines Hundreds of thousands of A microcomputer operating system.

Approximately 2,000,000 lines A military weapon management program.

(controlling missiles, for example) Several million lines 57

Software Development: A Broader View

• Measures of effort spent on real-life programs: Comparing programs by time – 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 58

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 59

Web Page Design Software: Dreamweaver

• 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 60

Web Page Design Software: Dreamweaver

• 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.

61

Web Page Design Software: Dreamweaver

• 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 62

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 63

Chapter Summary

• The Program Language Continuum 1. Hardware-wired programs 2. Human program a computer but require a program translation before the computer can perform a task 3. 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 64