CS101 Introduction to Computing Lecture 45 Review

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CS101 Introduction to ComputingLecture 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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readableprogram?
A program that is easy to read understand, and
therefore, easy to maintain enhance
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Readable programs are - more readable
- efficient enough
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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

• Read, understand the problem
• Do you have all the required data?
• No Get it
• Else assume it. State it explicitly
• Do the design
• Write test cases

• Write the code on a piece of paper
• Hand-check it
• Type it in
• Run check it on test cases
• Errors? fix redo 9
• 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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Todays 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
1.

• To build an appreciation for the fundamental
  concepts in computing

2.
To achieve a beginners proficiency in Web page
development
3.
To become familiar with popular PC productivity
software
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What value do computers bring?
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?

• fast

?
bored
?
storage
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What type of problems are not suitable for
computers
?
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Progression of Computer Technology

• Mechanical computing
• Electro-mechanical
• Vacuum tube
• Transistor
• (the current state-of the-art)
• 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, todays Webs content is designed for
  humans to read the Semantic Webs 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 users 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. ALUs, FPUs,
  Vector/SIMD units, etc.)

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Hardware
Operating System
Device Driver
Utility
Language Translator
Scientific Apps.
Business Apps.
Productivity Apps.
Entertainment Apps.
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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InterpretersImmediate response,butexecute
code slowlyCompilersCompiling takes
time,butsuper-fast execution
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Can a single language have all the good bits of
all other languages?
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Software Lifecycle
Concept Feasibility
User Requirements
Test
Developer Specs
Test
Planning
Test
Design
Test
Implementation
Test
Integration Testing
Opr. Maintenance
Acceptance Test
Retirement
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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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Caution! Caution! Heuristics dont 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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Dont just remove the defect correct the process
that caused it
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is a heuristic, an algorithm?
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When I look at a Web page it should
beself-evident, obvious, self-explanatoryI
should be able to get it - what it is how to
use it - without expendingany effort thinking
about itexcerpt from Steve Krugs book Dont
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 TrendsOn-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
1.
2.
To achieve a beginners proficiency in Web page
development
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 users browser about missing or
  incorrect data
• Reduced network traffic as the forms data is
  sent only once instead of many tos and fros

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Object A named collection of properties (data,
state) methods (instructions, behavior)
A collection of properties methods
All objects have the name property it holds
the name of the object (collection)
name
method 2
prop 1
prop 3
prop 5
prop 2
method 3
prop 4
method 1
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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
1.
2.
3.
To become familiar with popular PC productivity
software
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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
1.

• To build an appreciation for the fundamental
  concepts in computing

2.
To achieve a beginners proficiency in Web page
development
3.
To become familiar with popular PC productivity
software
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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