cs101- introduction to computing- lecture 45

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CS101 Introduction to Computing

Lecture 45Review & Wrap-Up

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During the last lecture we discussed Programming Methodology

• We looked at a few effective programming practices that result in the development of correct programs with minimum effort

• We also became familiar with testing & debugging

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readablereadableprogramprogram??

A program that is easy to read & understand, and therefore, easy to maintain & enhance

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Readable programs are:Readable programs are:

- - moremore readable readable

- efficient - efficient enoughenough

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Design Guidelines

• Break your code down into short and simple functions (e.g. take the 3 swap statements out from the last example and put them into a function of their own)

• Do not use global variables

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Coding Guidelines

• Indent blocks of code (2 to 5 spaces)

• Always use semicolons to end statements

• Identifiers:– Use the camelBack scheme– Make them descriptive but concise– Variables: nouns– Functions: verbs

• Comment liberally

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Guidelines for Developing Short Programs

1. Read, understand the problem

2. Do you have all the required data?

No: Get it

Else assume it. State it explicitly

3. Do the design

4. Write test cases

5. Write the code on a piece of paper

6. Hand-check it

7. Type it in

8. Run & check it on test cases

9. Errors? fix & redo 9

10. Done!

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Design & Code Reviews

• Probably the most efficient way of improving the a program

• Being humans, at time we see what is supposed to be there instead of what is actually there

• Another pair of eyeballs may not have the same problem, especially if they are were not involved in building the design or code

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Testing & Debugging

• Testing: The tasks performed to determine the existence of defects

• Debugging: The tasks performed to detect the exact location of defects

• Defects are also called bugs or errors

• Let us now look at one of their classifications

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Types of Errors

• Syntax errors

• Semantic errors

• Run-time errors

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Today’s Goal:(Review & Wrap-Up)

• To review some of the interesting ideas that we discussed over the last 44 lectures

• Please note that this lectures is not a comprehensive review, just a sampler!

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Course Objectives

To build an appreciation for the fundamental concepts in computing

To become familiar with popular PC productivity software

To achieve a beginners proficiency in Web page development

1.2.3.

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What value do

computers bring??

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fastbored

storage

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What type of What type of problems are problems are notnot suitable for suitable for computerscomputers?

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Progression of Computer Technology

1. Mechanical computing

2. Electro-mechanical

3. Vacuum tube

4. Transistor

(the current state-of the-art)

5. Quantum computing

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Quantum Computers

• Quantum computers may one day be millions of times more efficient than the current state-of-the-art computers …

• as their quantum mechanical nature will allow them to examine all possible answers to a question, simultaneously

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The World Wide Web

• A huge resource of info

• Logically unified, but physically distributed

• It is unlike any previous human invention:

– It is a world-wide resource, important to all and shared by all of the people in the world

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The Semantic Web

Whereas, today’s Web’s content is designed for humans to read; the Semantic Web’s content will be designed for computers to understand meaningfully

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Internet: Network of Networks

• A large number of networks, interconnected physically

• Capable of communicating and sharing data with each other

• From the user’s point view, Internet – a collection of interconnected networks – looks like a single, unified network

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Language of the Internet: TCP/IPTransmission Control Protocol/Internet Protocol

• TCP breaks down the message to be sent over the Internet into packets

• IP routes these packets through the Internet to get them to their destination

• When the packets reach the destination computer, TCP reassembles them into the original message

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Instant Messaging

• eMail: Slow response times

• eMail: No way of knowing if the person we are sending eMail to is there to read it

• eMail: The process of having a conversation through eMail by exchanging several short messages is too cumbersome

Instant messaging (IM) solves these problems

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Why use many not-so-powerful processors working in parallel

Why not just design a single, really powerful processor

?

?

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On-Chip Cache Memory• That small amount of memory located on the

same chip as the uP

• The uP stores a copy of frequently used data and instructions in its cache memory

• When the uP desires to look at a piece of data, it checks in the cache first. If it is not there, only then the uP gets it from the main memory

• Its proximity to the uP makes access times short

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Ways of Enhancing A uP• Increase the clock frequency

• Increase the word-width

• Improve the effectiveness of the caching algorithm

• Add more functional units (e.g. ALU’s, FPU’s, Vector/SIMD units, etc.)

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Hardware

Operating System

UtilityLanguageTranslator

Device Driver

ScientificApps.

BusinessApps.

ProductivityApps.

EntertainmentApps.

System software

Application software

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The Role of An OS

• Manages the HW and SW resources of the computer system, often invisibly. These include the processor, memory, disk drives, etc.

• Provides a simple, consistent way for applications to interact with the HW without having to know all the details of the HW

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Who Owns Software?

• Generally, although a piece of SW that is being used by millions, it is not owned by any of them!

• When we buy a SW package, we do not really buy it – we just buy a license that allows us to use it, the ownership stays with the maker

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4th-generation languages

High-level languages

Assembly languages

Machine languages

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Interpreters:Immediate response,

butexecute code slowly

Compilers:Compiling takes time,

butsuper-fast execution

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Can a single language have all the good bits of all other languages?

Concept & Feasibility

User Requirements

Developer Specs

Planning

Design

Implementation

Integration Testing

Opr. & Maintenance

Retirement

Test

Test

Test

Test

Test

Acceptance Test

Software Lifecycle

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Algorithm

1st Definition:Sequence of steps that is taken

to solve a problem

Better Definition:A precise sequence of a limited

number of unambiguous, executable steps that terminates in the form of a solution

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Pseudo Code

• Quite suitable for SW development as it is closer in form to real code

• One can write the pseudo code, then use it as a starting point or outline for writing real code

• Many developers write the pseudo code first and then incrementally convert each line into real code

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Heuristic

Common sense lesson drawn from experience

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CautionCaution!! CautionCaution!! Heuristics don’t always lead to the best results

At times they even lead to the wrong ones, but mostly to results that are good-enough

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Don’t just remove the defect; correct the process that caused it

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is a heuristic, is a heuristic, an algorithman algorithm??

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When I look at a Web page it should beself-evident, obvious, self-explanatory

I should be able to ‘get it’ - what it is &how to use it - without expending

any effort thinking about it

excerpt from Steve Krug’s book Don’t Make Me Think

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Avoid using pictures that are strictly decorative

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(Artificial) Intelligent Systems

SW programs or SW/HW systems designed to perform complex tasks employing strategies that mimic some aspect of human thought

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Not a Suitable Hammer for All Nails!

if the nature of computations required in a task is not well understood

or there are too many exceptions to the rules

or known algorithms are too complex or inefficient

then artificial intelligent systems have the potential of offering an acceptable solution

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Database

• A collection of data organized in such a fashion that the computer can quickly search for a desired data item

• All data items in it are generally related to each other and share a single domain

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Relational Databases

• Databases consisting of two or more related tables are called relational databases

• A relational database stores all its data inside tables, and nowhere else

• All operations on data are done on those tables or those that are generated by table operations

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Future Trends:On-Demand Computing Power

• Almost infinite “computing power” supply

• Reliable, maintenance-free, just like the electricity, telephone, or water-supply service

• No capital expenditure; you pay for only what you use!

• Same will be true for storage

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Future Trends: Immortal Minds

• Some day it will be possible to load all the lectures, papers, books and SW produced by an expert into an intelligent system

• After that system processes, indexes and restructures the info in those artifacts, it will be possible to have a conversation in plain English (or some other language) with that system

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Distances Are Contracting!Distances Are Increasing!

• Because of the ever-decreasing costs of verbal, text, video communications, it is becoming easier to stay in touch of anyone, regardless of their physical location

• Solitude is the order of the day as many children & adults spend their free time surfing, chatting, playing computer games, instead of spending it on interacting with friends or family

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Computers may Become too Powerful!

• Computers keep on becoming more and more powerful, gaining more and more autonomy

• They are being equipped with fail-safe and self-healing technologies

• Are we heading towards a future where the role of the masters and the slaves will be reversed?

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Course Objectives

To achieve a beginners proficiency in Web page development

1.2.3.

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Why JavaScript?

• HTML is great for static Web pages; however, supports only rudimentary interactivity through forms and hyperlinks

• JavaScript can be used (along with HTML) to develop interactive content for the Web

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Some of things that JavaScript cannot do!

• The following file ops. on the client computer:– Read -- Modify– Rename -- Delete– Create

• Create graphics (although, it does have the ability to format pages through HTML - including the placement of graphics)

• Any network programming bar one function: the ability to download a file to the browser specified through an arbitrary URL

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Advantages of Client-Side Scripting

• Reduced server load as it does not have to send messages to the user’s browser about missing or incorrect data

• Reduced network traffic as the form’s data is sent only once instead of many to’s and fro’s

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Object: A named collection of properties (data, state) & methods (instructions, behavior)

prop 1

prop 2prop 5

name

prop 3

prop 4

A collection of properties & methods

All objects have the “name” property: it holds the name of the object (collection)

method 3method 1

method 2

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Functions

• A named group of statements that is put together once and then used (by reference) repeatedly on a Web page

• Code becomes easier to read, understand and maintain

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Local and Global Variables

Local or Function-level Variable

Effective only in the function in which they are declared

Global Variables

Visible everywhere on the Web page

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Image Preloading

• The Image object can be used to download an image into the cache before it is actually needed for display

• This technique can be used to create smooth animations or to display one of several images based on the requirement

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Course Objectives

To become familiar with popular PC productivity software

1.2.3.

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Productivity SW

• The lectures and assignments were designed to give a brief introduction, and no more

• All we desired was for you to become able to open the package and perform some trivial tasks

• With time, you will find more and more use for these packages, and gradually develop an expertise that later will become very useful in your career

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Course Objectives

To build an appreciation for the fundamental concepts in computing

To become familiar with popular PC productivity software

To achieve a beginners proficiency in Web page development

1.2.3.

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• How successful were we in helping you achieve those objectives?

• Please do let us know so that we can modify the future offerings of this course accordingly. I will be most grateful

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• I have enjoyed doing this course with you very much

• Hope it was enjoyable & useful for you as well

• I thank you for your attention and especially for your eMail & discussion board messages

• A good number of those messages were quite informative and I thank you for sharing that info with me

• Until the next time when we meet …