Workshop for Programming And
Systems Management Teachers
Chapter 1
Introduction to Computers and
Programming
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Learning Goals
• Understand at a conceptual level
– What is a computer?
– What are the parts of a computer?
– What can computers do?
– What is a program?
– Why learn to program?
– What is hard about learning to program?
– What is hard about teaching programming?
– Strategies for teaching programming
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What is a Computer?
• One who computes
• A device that performs
high-speed mathematical
and/or logical operations
or that assembles, stores,
correlates, or otherwise
processes information.
• The first computers were
people
– who did computations
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Parts of a Computer
• User Interface
– monitor (screen),
mouse, keyboard,
printer
• Brain - Central
Processing Unit
– can do math and logic
operations
• Memory - Storage
– main - RAM
– secondary – Disks,
CD-ROMs, DVDs
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CPU – Brain of the Computer
• Arithmetic/Logic Unit
(ALU)
– Does math and logic
calculations on
numbers in registers
• Control Unit
– Reads instructions
from memory and
decodes and executes
them using the ALU
345
263
608
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Add register A
to register B
Store the value
in register C into
memory location
320843202
Fetch, Decode, Execute Cycle
• The control unit reads (fetches) an
instruction from memory
• The control unit decodes the instruction
and sets up the hardware to do the
instruction
– like add the values in the A and B registers
and put the result in the C register
• The instruction is executed
• The program counter is incremented to
read the next instruction
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Processor Speed
• Processors (CPUs) have
a clock
• Clock speed is measured
in megahertz (MHz) or
gigahertz (GHz)
• Some instructions take
just 2-3 clock cycles,
some take more
• When the clock speed
increases the computer
can execute instructions
faster
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Memory
• Computer memory is
used to store data
• The smallest unit of
memory is a bit (Binary
digIT)
• A bit can be off (no
voltage) or on (has
voltage) which we
interpret to be 0 or 1
• Memory is organized into
8 bit contiguous groups
called bytes. A megabyte
is 1,048,576 bytes (over 1
million bytes). A gigabyte
is over 1 billion bytes.
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How does Memory Represent Values?
• The different patterns of the on and off bits in a
byte determine the value stored
• Numbers are stored using binary numbers
– 101 is 1 * 20 + 0 * 21 + 1 * 22 = 5
• Characters are internally represented as
numbers
– Different numbers represent different characters
– There are several systems for assigning numbers to
characters:
• ASCII, EBCDIC, and Unicode
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Encodings Make Computer Powerful
• Voltages are interpreted as numbers
• Numbers can be interpreted as characters
• Characters can be interpreted to be part of
a link to Sun’s Java Site
<a href=http://java.sun.com>Sun’s Java Site </a>
a
0100 0001
off on off off off off off on
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Notepad Exercise
• Open notepad and
type a sentence in it
• Save the file
• Check the size in
bytes by leaving the
cursor over the file
name
• Now count the
number of letters and
spaces
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Binary Numbers
• We usually work with decimal numbers
with digits from 0 to 9 and powers of 10
7313 = (7 * 1000 + 3 * 100 + 1 * 10 + 3 * 1)
Or (7 * 103 + 3 * 102 + 1 * 101 + 3 * 100)
• The binary number system uses digits 0
and 1 and powers of 2
0101 = (0 * 23 + 1 * 22 + 0 * 21 + 1 *20)
(0 * 8 + 1 * 4 + 0 * 2 + 1 * 1) = 5
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Binary Addition
• To add two decimal
numbers you add the
digits and if the total is
greater than ten you carry
the one into the next
column
• To add two binary
numbers
– 0+0=0
– 0 + 1 and 1 + 0 = 1
– 1 + 1 = 0 with a carry of 1
into the next column to the
left
00
01
---01
10
01
--11
00111001010
01010101101
------------------10001110111
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111
001
-----1000
2’s Compliment Notation
• Computers actually only know how to add
– So, how do they handle subtraction?
• Computers subtract by adding a negative
number
• How do you represent a negative number
in memory?
– Positive numbers in 2’s compliment are just
the same as a binary number
– For negative numbers reverse 0s and 1s and
then add 1
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2’s Compliment Example
• To subtract 3 from 7
• First represent both as a binary number
– 7 is 0000 0111
– 3 is 0000 0011
• Reverse the 0s and 1s and then add 1 to
get -3
– 0000 0011 reversed is 1111 1100
– add 1
0000 0001
– The result is
1111 1101
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Add the Negative Number
• To subtract 3 from 7
• Add -3 to 7
– 7 is
– -3 is
– The result is
0000 0111
1111 1101
1 0000 0100
• Through away the leftmost 1
• The answer is 0000 0100 which is 4
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Patterns Exercise
• How many different patterns of on and off
bits are there in 3 bits? How many in 4
bits? How many in 8 bits?
• 000 is one pattern
• 001 is another pattern
• 010 is another pattern
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Does the number of patterns matter?
• Some garage door
openers in the 70s
used 8 bits to set the
code to use to open
the door
– Giving 256 different
patterns
– Which is enough that
you won’t open your
neighbors door
– But small enough that
someone could try
each one
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Remote Entry Systems
• With 8 bits for a code you
have a 1/256 chance of a
random code working
– You don’t want someone
opening your car in a place
with lots of cars (like a
mall)
• There are also radio
scanners that can capture
your code
– So you want the code to
change each time
• Modern remote entry
systems use a 40 bit
rolling code
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Types of Memory
• Registers
– Very high speed temporary storage areas for use in
the CPU
• Cache
– High speed temporary storage for use with the CPU
• Main Memory – Random-access Memory (RAM)
– High speed temporary storage
– Contains programs and data currently being used
– Often described in Megabytes (MB)
• Secondary Memory - Disks
– Contains programs and data not currently being used
– Often described in Gigabytes (GB)
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Why are there so many types of memory?
• The faster memory is the more it costs
– So we reduce the cost by using small
amounts of expensive memory (registers,
cache, and RAM) and large amounts of
cheaper memory (disks)
• Why do we need cache?
– Processors are very fast and need quick
access to lots of data
– Cache provides quick access to data from
RAM
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What can Computers Do?
• Add, subtract, multiply, and divide
numbers in registers
• Logic operations on numbers in registers
– Less than, greater than, equal to
– When true jump to a new instruction
• Move data between types of memory and
to other input and output devices
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Vocabulary Exercise
• Look at two computer
advertisements
• See if you can figure out what all
the words mean
• Use the internet to look up
unfamiliar words
– http://computer.howstuffworks.com/
– http://en.wikipedia.org/
– http://webopedia.com
• Which one is a better for
computer games?
• Which one is better for your
homework?
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What is a Computer Program?
• Instructions to a
computer that allow it
to process some data
• You can think of it like
a recipe
– It contains instructions
– Processes ingredients
to produce a result
– You can use the same
recipe over and over
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Computer Languages
• Each processor has its own language
– Machine language
– 0001 may be the instruction for adding two registers
• Assembly language is a low-level language
– Has the same instructions as machine language but
allows people to use names for the instructions
instead of numeric codes (like ADD)
– An assembler translates the names into the numeric
machine language
– Executes very fast
– Slow for programming
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Programming is About Naming
• Computers can associate names with
anything
– A byte
– A group of bytes
– A group of letters
– A file
– A picture
– A program, recipe, or function (method)
– A type (class)
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File Names
• Operating systems
associate file names with
locations on your hard
disk
– A hard disk stores values
even after the power is
turned off
• When you double click
on a file
– The operating system
reads the data starting at
that location into RAM
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Names for Values
• When work with data in main memory we
will usually assign a name to it.
– Rather than remember the address in
memory
• The computer associates the name with the
address for us
• Programs are like algebra
– Where you use names to make the equations
make sense
• PV=nRT or e=Mc2
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Programs are for People
• The computer doesn’t care what names
we use
• The names are important so that our
programs are understandable
– To us
– To others
• Names should be appropriate
– Not too long or confusing
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High Level Languages
• Are translated (compiled) into machine
language or assembly language
• Contains more instructions than in the
original machine language
– Which translate into several machine
language instructions
• May have slower execution speed than an
assembly language program
• Easier and faster for writing programs
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Programming Languages
• A set of names that have encodings
– Some names allow us to define new
encodings
• You can assign a name to represent a
value (we call this a variable)
• You can assign a name to represent a
function or procedure
• You can assign a name to a collection of
related variables and functions/procedures
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FORTRAN
• Acronym for formula translator
• The first high-level language
• Developed in the 1950s at IBM by John
Backus
• Mostly used for scientific applications that
require extensive mathematical
computations.
• There have been several versions
• The most recent is FORTRAN-90
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COBOL
• Acronym for common business oriented
language.
• Developed in the late 1950s and early
1960s by the Conference on Data
Systems and Languages (CODASYL).
• Popular for business applications that run
on large computers
• Meant to be easy to read
– Very wordy to program
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BASIC
• Acronym for Beginner's All-purpose
Symbolic Instruction Code.
• Developed in the mid 1960s at Dartmouth
College by John G. Kemeny and Thomas
E. Kurtz
• Mostly used in business and education
• VisualBasic is a form of BASIC created by
MicroSoft that uses visual programming
– Good for graphical user interfaces
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RPG
• Originally meant Report Program Generator
– but as of 1998 with RPG IV (RPG/LE) it is no longer
an acronym
• Originally developed in 1965 to generate reports
from data files and databases
– Not as verbose as COBOL
– More functionality than BASIC
• Has evolved into a procedural programming
language
• Used on IBM and DEC minicomputers
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C
• Developed by Dennis Ritchie at Bell Labs
in the mid 1970s
• Originally a systems programming
language
– Closer to machine language than other highlevel languages
– Used to develop the UNIX operating system
• Popular in business and science in the 80s
• Used on personal computers because took less
memory than other computer languages
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C++
• Developed by Bjarne Stroustrup at Bell
Labs in 1986
• Added object-oriented features to its
predecessor, C.
• Very popular in the late 80s to 90s
• Popular for 3-d graphics
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Java
• Developed at Sun in the early 1990s
– Invented by James Gosling
• Similar to C++ in syntax but easier to use
– Java is C++ --
• Cross-platform, object-oriented language
• Used in business, science, and education
• One of the fastest adopted technologies of
all time
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C#
• Microsoft developed object-oriented
language for the .NET platform
• Created by Anders Hejlsberg (author of
Turbo Pascal and architect of Delphi), Scot
Wiltamuth, and Peter Golde
• Similar to Java
– Garbage collection
– No explicit pointers
– Doesn’t compile to machine language
• Common language runtime (CLR)
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Which Language?
• All high-level languages are eventually
translated into machine language
• You can write the same program in any
language
– The computer doesn’t care what high-level
language you use
• The language matters to the programmer
– How long does it take to write the program?
– How hard is it to change the program?
– How long does it take to execute?
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Why Don’t We Just Use English?
• English is good for
communication between two
intelligent humans
– Even then we sometimes don’t
understand
• Computers are very stupid
– They basically know how to
add, compare, store, and load
– Programs are very detailed
instructions
• Everything must be precise and
unambiguous
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Programming Exercise
• Write down
instructions for how to
play checkers
• Have another group
read the directions
and do the actions
– stop anytime anything
isn’t clear and ask for
clarification
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Why Learn to Program?
• Alan Perlis, first head of Carnegie Mellon's
Computer Science Department, made the claim
in 1961 that computer science, and
programming explicitly, should be part of a
liberal education
• Seymour Papert claimed in the 70’s and 80’s
that learning to program is “learning to think, and
debug one’s own thoughts.”
– If you learned to program, you learned to plan, to
debug, to handle complexity, etc.
• Twenty years of research found that that is
simply not true.
• Most people don’t learn to program
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What CS Education Research Tells Us
• Most people don’t learn to program in one
semester
– Alan Perlis, “Most people find the concept of
programming obvious, but the doing impossible.”
• Many people find CS classes boring and
irrelevant
• Most people can’t transfer what they learn in
programming
• Students have a hard time putting statements
together to accomplish a task
• Students learn much less than teachers think
they will
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So, Why Learn to Program?
• The computer is the most
amazingly creative device
that humans have ever
conceived of. If you can
imagine it, you can make
it “real” on a computer.
• Computers will continue
to have a major impact on
modern life
– Movies, games, business,
healthcare, science,
education, etc
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Computers Are Commonplace
• Computers, or at least
processors, are in
many common
devices
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Programming is Communicating
• Alan Perlis, “You think
you know when you
can learn, are more
sure when you can
write, even more
when you can teach,
but certain when you
can program.”
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What is Hard About Programming?
• It is easier to write an incorrect program than
understand a correct one – Alan Perlis
• Beginners have a hard time understanding some
of the core concepts
– Boolean expressions with more than two items
• if (a < b) is okay
• if (a < b && c > d) is hard
– Iteration (loops)
• Beginners have a hard time putting statements
together to accomplish a task
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Strategies for Teaching Programming
•
•
•
•
•
•
•
Do Live Programming
Choose Depth over Breadth
Assign Interesting Programs
Use Pair Programming
Start by Modifying Programs
Have Lots of Small Projects
Go from Concrete to Abstract
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Do Live Programming
• Program in front of the
students and talk about
what you are doing and
why you are doing it
– Programming is a new and
strange activity for most
people
– Talk through the algorithms
and how to translate them
to code
– Let them see you make
mistakes and fix them
– Learn by example
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Choose Depth over Breadth
• Cover difficult topics
in depth
• Cover topics in more
than one way
• Try to get people to
connect the concept
to something they
already know to
reduce “brittle
knowledge”
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Assign Interesting Programs
• A basic problem is
that students find
programming projects
irrelevant
• Use motivating,
relevant examples
and projects
– Games, digital video
special effects,
animation, graphics,
pictures, sound, web
pages, simulations
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Use Pair Programming
• Have two students
work together on
programs
• They can explain
what they are thinking
to each other
– Learn from each other
• One may be better at
typing
– Reducing frustration
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Start by Modifying Programs
• Students won’t have to remember everything at
once
–
–
–
–
Just focus on the part they are trying to understand
Less daunting than starting with nothing
Just getting the syntax right is time consuming
Reading code is a valuable skill
• The given code provides a sample of good
coding practice
– Teach by example
– Gives advanced students something to learn from
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Lots of Small Projects
• Programming is a skill
– It takes practice
• Getting the program to work
– Is frustrating while you are working on it
– Rewarding when it works
• Students take much longer to program
than teachers estimate
– Expert programmers are much, much faster
than beginners
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Go from Concrete to Abstract
• Use props, live demonstrations, role
playing
– People learn better when you start with
concrete things and later introduce abstract
ideas
• Try to link concepts to students lives
– To make it relevant
– Reduce brittle knowledge
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Summary
• Computers are fairly simple machines
– Fancy calculators with lots of storage
– But incredibly fast
• Computers have changed modern life
• Programs are instructions to a computer to
accomplish a task
• Programs written in high-level languages are
translated to machine or assembly language by
a compiler
• Programming is hard to learn
– But there are some ways to make it easier
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