2012 CSE-BEACON camp1 Computer Science Concepts 1. What is an algorithm? 2. Binary information coding 3. Programming concepts via Scratch Designed for

2012 CSE-BEACON camp 1

Computer Science Concepts

1. What is an algorithm?2. Binary information coding3. Programming concepts via

ScratchDesigned for learners 10 years old up to 100.

Materials for hands on activities


1) a set of cards with numbers, say, 42, 17, 43, 55, 20, 32, 122) A set of cards with binary place values: 1, 2, 4, 8, 16

3) Scratch downloaded from www.scratch.mit.edu

4) www.learnscratch.org for tutorials for homework

5) www.cse.msu.edu/~stockman for this and other ppt sets


What is an algorithm?

What is an algorithm? Algorithms for average and min

An algorithm for sorting


Algorithm for computing the average of two numbers

Let the first number be A; say A=12 And the second number be B; say B=15 To compute the average _____________ So the average of 12 and 15 = ________ WHAT IS THE AVERAGE ALGORITHM?


What is an algorithm?

An algorithm computes some output from the given input using precise steps that a machine can follow (machine or other agent)

Hands on activity: finding MIN

Organize into 2-person teams Team has “person A” and “person

B” Each team has a stack of cards There is one number on each card No one looks at numbers yet



problem: finding min Person B is the “worker” for A. Person A has cards, but cannot look at the

numbers. A must find the min of all cards. B can look at only 2 numbers at a time --

B returns to A the smaller smaller first. HOW CAN PERSON A FIND THE MIN? Shuffle the cards A and B switch roles: new person A finds

MIN


review: team finding the min Person A can look at no numbers! No numbers can be seen by A, EVER! Person B can look at only two numbers on

cards given by person A. Person B gives back to A first the card with the

smaller number (if numbers are = then it doesn’t matter which is given first)

Person A must find the min and show it to the instructor WITHOUT EVER SEEING IT

A and B should switch roles and repeat.

Thought Questions If A has 10 cards with numbers, how

many times does A call on B? _____ If A has 100 cards, how many times

does A call on B? _____ If A has N cards, how many times

does A call on B? _____ Finding the MIN of a list of numbers

has “complexity” _______


Thought Question

Suppose A has 2 assistants – B and C

Can A find the MIN any faster? HOW?

Computers and computer programs can be structured to do more than one operation at a time.



Problem: how to sort?

Use set of cards for each team. How can A sort using B

as comparer?TRY IT: instructor will check

your final output


Sorting two-person activity This is a 2-person exercise. Person A CANNOT

see the numbers – EVER! To solve the sorting puzzle, person A must form

an ordered list of cards, which the instructor will check for order (this is the OUTPUT).

Person B can only compare two numbers by seeing the numbers. Person B gives A the smaller number card first (precise operations).

Person A can only ask Person B which of two cards has the smaller number. Person A never ever looks at any numbers.

To solve the sorting puzzle, person A must start from an unordered list of cards (this is the INPUT).


Sorting thought questions How many times will A call on B to sort 10

numbers? _____ How many calls to sort 100 numbers?

_____ How many calls to sort N numbers? _____

There are many sorting algorithms. Some are fast when N is small but slow when N is big. Some are the opposite. Computer scientists learn these algorithms and many others.

Algorithms often do operations over and over

Called “looping” Also called “iteration” or

“repetition” “Recursion” is a related idea – first

select the MIN from the list and then “recurse” on the rest of the list



Binary Information Coding

1. Only 2 symbols: WHY?2. Can we code numbers,

characters, music, images, movies, car designs using just 2 symbols?

Coding activities

1. Guessing the number of fingers in decimal2. Guessing 1 finger versus 0 fingers3. Encoding small integers using binary cards4. Coding using animate versus inanimate

objects (“My teacher plays rock, paper, scissors with me.”)

* Instructor quickly brings, say, 7 fingers from behind the back. Students make errors in guessing the number. Few errors in 0 versus 1 discrimination.


Fundamental coding principle

Can rep 2 “things” with 1 bit: yes/no; smiley/sad; high/low; odd/even

Can rep 4 “things” with 2 bits; 00:clubs; 01:diamonds; 10:hearts; 11:spades

Can rep 8 things with 3 bits 0 00 1 00

0 01 1 01 0 10 1 10 0 11 1 11


Fundamental coding principle

Each time we add one more bit, we __________ the number of binary strings

There are _____ binary strings of length N=7 (think about ASCII code)

There are thus ______ possible binary strings of length N bits



ASCII code for characters

CHAR CODE CHAR CODE

A 001000001 a 001100001 B 001000010 b 001100010 C 001000011 c 001100011 + 000101011 . 000101110 * 000101010 % 000100101

How many characters does a computer need to use?

Old Univac system used 6 bit char – a design disaster: _____ symbols max

IBM 8-bit code enabled ____ symbols (digits, caps, small letters, punctuation, graphic symbols, bell, null, etc.)

Unicode uses 16 bits to code all of the above and international characters:

______ symbols.



CD has many tracks of spots

Shiny spot is 0 Burned spot is 1 5 billion spots total 700 MB total 44,000 x 16 spots

for just 1 second of high fidelity music

Laser reads shiny versus dull spots

CD

CD spins

What’s a “CD”?

Even parity to detect errors

To the 7-bit ASCII code, append one parity bit to have an even # of 1 bits

Sender always sends an even number of bits

If some disturbance causes a bit to change, receiver gets an odd number or 1-bits in the char code.

If error, receiver asks for retransmit.


Bit strings as numbers

Binary Places Decimal equivalent

16 8 4 2 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 1 0 2 0 0 1 1 1 7 1 0 1 0 1 21



Binary Ops easy for machine Addition has few

rules.

Multiplication has few rules

These can be carried out in nanoseconds by computer circuits

0+0 = 0 0+1 = 1+0 = 1 1+1 = 0 with 1

carry

0x0 = 0x1 = 0 1x0 = 0 1x1 = 1

1 is 0 is

What number?

What number?

What number?

252012 CSE-BEACON camp

0 is 1 is

What number? ____

What number? ____

What number?


0 is 1 is

What number? ______

What number? ______

What number? ______

What number? ______


Binary coding in a computer

Symbol 0 can be represented by +5V and 1 by -5V

0 can be darkness and 1 lightness, as used on CDs and DVDs or in optical fibers



Conversion of decimal to binary: Algorithm #1

Let D1 be a decimal integer

Let R1 = remainder of D1 divided by 2; R1 is the 1’s bit

Let D2 be the dividend of D1/2

Let R2 = remainder of D2 divided by 2; R2 is the bit in the 2’s place. & so on

Decimal to binary conversion


INPUT: a decimal numberOUTPUT: a binary numberPRECISE STEPS: repeated division by 2; recording the remainderTERMINATES?: always (why?)CORRECT?: why?

Guessing games


• Guessing birthdays: just day of month• Guessing month and day • Guessing face value of cards• Guessing suit and face value

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Programming concepts via Scratch

Free download of software available atwww.scratch.mit.eduVideo tutorials for learning available atwww.learnscratch.org


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What can we do with Scratch?

• Learn some computing concepts.• Learn some practical algorithms.• Use Scratch as computing tool.• Have fun with Scratch creating

stories, games, art.


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Start scratch and let’s go!

• In the lab, Click on the cat icon

• Scratch programming environment comes up

• First do simple things


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Explore Scratch environment

• Stage is at upper right (where actors act and information is displayed)

• Sprite is another name for actor.• Instruction menus/panel at left

(instructions for the actors)• A script is another name for program or

method; a script tells the actor what to do.

• Programming area in center; here is where we construct scripts for the sprites


The VARIABLES Menu Implement an average algorithm Make a variable “FIRST” and set it to 12 Make a variable “Second” and set to 15 Make variable “Average” Use OPERATIONS Menu to set the

Average to (FIRST+SECOND)/2 Test Scratch and algorithm


Square root by repetition Guess sqrt(N) to be 1.0 Set root1 = 1.0 (first factor) Set root2 = N/root1 (second factor) root1 is not likely to = root2 Reset root1 to the average of root1 and root2

(it will be in between them, why?) Reset root2 = N/root1 Repeat all of the above until root1 and root2

are “very close”


Algorithm study is RICH! Algorithm to find your BEST mate? What if you had the coding of genes for

all possible mates? Algorithm to make bet on Big 10 game? Algorithm to find best molecule to bond

with a given input molecule? Algorithm to bond 2 molecules to create

“best properties”.


Information theory is RICH

SETI: Search for Extra Terrestrial Intelligence

Jodi Foster movie “Contact” What are the chances that a

random signal from space codes “I love you”? Or “X^2+Y^2 = R^2”?


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The LOOKS menuHas instructions for setting the

color, size, and visibility of a sprite. Costumes will be used later.


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The “hello” script (program)

• Choose the Looks menu• Click on the “say hello” lego block• Check your sprite behavior at the

right• Then click “say hello for 2 secs”

Your very first Scratch program!


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Try some other looks operations (click on menu items)

• Change color effect by 25• Change color effect by 25 again• Hide• Show• Change size by 10• Change size by 10 again• Set size to 100%


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Let’s write a script to

• Say “hello” for 2 seconds• Then change color by 25• Then think “Hmm..” for 4 seconds• Then change color by 75• Then change size by 200

Drag each instruction from the menu to the center script area. Connect them into a single block. Edit the parameters to get the numbers we want.


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Our script (program)


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A sequence or block is a simple script or program

• The first instruction is done first• The second instruction is done

second• The last instruction is done last.• (if any one instruction is done, then

every on of them is done)


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The WAIT instruction

• WAIT is needed to slow down the acting so we can see or hear it properly (computers are too fast sometimes)

• Get the wait instruction from the CONTROL menu. Ignore the other menu options for now.

• Insert a wait in our looks script


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3 second pause between changing color and size


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Student exercise: write a script to do the following

• Double the size of the sprite• Wait 2 seconds• Change the color of the sprite to

green• Wait 4 seconds• Change the whirl effect to 100• Say “That’s all folks!”


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The MOTION menuHow to locate and orient a sprite; and, how to move a

sprite.


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Position on the stage

• Using the Looks menu, shrink our cat to 25%.

• Click on the Motion menu.

• Click to check the box for x-position and y-position

Drag your cat around and note its x-y position.


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Exercises: goto instruction(do you know about coordinates?)

• In the Motion menu, drag the “goto xy” instruction to the script panel.

• Edit the coordinates and click to see the sprite’s position

• A) goto x=200, y=0• B) goto x=-200, y=0• C) goto x=200, y=-100

Where does the cat go?


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The “glide-to” instruction

• Drag the “glide-to” instruction into your script panel.

• Edit the coordinate values and click to see where your sprites goes.


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Exercise

• Create a script to glide the sprite along the sides of a triangle. The first vertex of the triangle is (-100, -100). The second vertex is (200, -100). The third vertex is (50, 100). Make sure you complete the triangle.

• Change the speed of gliding and run again.

• New feature: click on Pen Down in the Pen Menu and run it again


Exercise: A fun looping program

Position your sprite at the lower left Put the pen down Do the following forever Rotate +5 degrees Move around an equilateral triangle

as before (turning 120 degrees each angle)


Exercise: bat flying randomly


Make a bat fly by flapping between 2 bat “costumes”. Use random values of coordinates x and y.Use arrows keys to control the bat’s position.* Use a forever loop to make the bat continue to fly when the flag is clicked* See if you can create a “score” variable and use it to count how many times the user clicks on the bat.

Exercise: find the MIN of a list

Explore how to create a list variable

Explore how to input numbers to the list

Explore how to pass through the list to set a variable MIN to the minimum in the list

Some hints follow2012 CSE-BEACON camp 56

Make list L and also a variable for its Length

Our list


Ask the user for list length after the user hits key ‘L’


Repeat Length times, ask the user for item k of the List

The user has given 3 items and is being asked for item k=4.


Documents

2012 CSE-BEACON camp1 Computer Science Concepts 1. What is an algorithm? 2. Binary information coding 3. Programming concepts via Scratch Designed for