Virtual University Course CS101- Introduction to Computing Lecture No 45 Review & Wrap up

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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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readablereadable
programprogram??
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 readablereadable
- 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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fast

bored
storage

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What type ofWhat type of
problems areproblems are notnot
suitable forsuitable 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/IP
Transmission 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
Utility
Language
Translator
Device Driver
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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Interpreters:
Immediate response,
but
execute code slowly
Compilers:
Compiling takes time,
but
super-fast execution

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

32. 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 be
self-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 2
prop 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 …