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An intro to Scratch Notes and Tasks for ITEC-I5 Camp Leaving lots of exploration for the future. ITEC-I5 Scratch Aug 2009 1 What are our goals? Learn some computing concepts. Use Octave as computing tool. Use Scratch as computing and multimedia tool. Have fun with Scratch creating stories, games, art. Learn some computing concepts. ITEC-I5 Scratch Aug 2009 2 Who computes? Scientists Engineers Businessmen Social scientists Artists FBI agents Brain surgeons Grandkids ITEC-I5 Scratch Aug 2009 3 Monday concepts (20 min) What is an algorithm? An algorithm for an average and min An algorithm for sorting ITEC-I5 Scratch Aug 2009 4 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 = ________ ITEC-I5 Scratch Aug 2009 5 What algorithm for the average age of two people? Input this Do precisely this Do precisely that Output what 12 15 ITEC-I5 Scratch Aug 2009 6 problem: finding min Person B is the “ref” watching A. Person A has list of numbered cards, but cannot look at all the numbers. A can look at 2 numbers at a time only -- one card in each hand. A must find the min of all cards. Exchange roles, with A the “ref” and B “the player”. HOW TO ALWAYS FIND THE MIN? ITEC-I5 Scratch Aug 2009 7 Problem: 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. ITEC-I5 Scratch Aug 2009 8 Problem: how to sort? Use set of cards for each team. How can A sort using B as comparer? ITEC-I5 Scratch Aug 2009 9 Sorting two-person game This is a 2-person exercise. 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). ITEC-I5 Scratch Aug 2009 10 Sorting by selecting minimum Spread out list of number cards 31, 22, 13, 32, 11, 21, 23, 33, 12 Select the minimum and begin a new list 11 Select the min of what’s left and add it to the end of the new list. 11, 12, Repeat this process until the original list is empty and the new list has all the cards. 11, 12, 13, 21, 22, 23, 31, 32, 33 ITEC-I5 Scratch Aug 2009 11 Problem: what is the average age of our class? How do we define this? ..compute this? An algorithm computes some output from the given input using precise steps that a machine can follow ITEC-I5 Scratch Aug 2009 12 Students use Octave (10 min) Verify the work and problem solutions as below [while the instructor leads]. ITEC-I5 Scratch Aug 2009 13 Compute the average of two numbers using Octave sum is a variable; sum = 12 + 15 set its value to sum = 27 12+15 average = sum/2 average is another average = 13.500 variable; set its value to the value of sum divided by 2 ITEC-I5 Scratch Aug 2009 14 Octave has many useful ops It can operate on numbers -- +, /, sqrt It can operate on lists of numbers – min, max, length, mean Use Octave as needed in camp and after! ITEC-I5 Scratch Aug 2009 15 gKids = 10 13 11 12 13 >> length(gKids) Precise steps to You can use the ans = 5 ages of the actual compute the group present. output from the >> sum(gKids) input. The input is the ans = 59 list of ages; the output is the >> avgAge = sum(gKids)/length(gKids) average of all the ages in the list. avgAge = 11.8000 ITEC-I5 Scratch Aug 2009 16 sort a list into order >> gKids gKids = 10 13 11 12 What algorithm does 13 MATLAB use to sort the >> sort(gKids) list? ans = 10 11 12 13 13 What algorithm finds >> min(gKids) the min? ans = 10 What algorithm finds >> max(gKids) the max? ans = 13 >> ITEC-I5 Scratch Aug 2009 17 There are MANY sorting algorithms. Recursively selecting the min is a BAD algorithm when the list is big. Computer scientists know many different algorithms, some good for small and some good for big lists. ITEC-I5 Scratch Aug 2009 18 Start scratch and let’s go! (90 min) Click on the cat icon If not on desktop, download from www.scratch.mit.edu Scratch programming environment comes up quickly We will first do simple ops ITEC-I5 Scratch Aug 2009 19 Goals for Scratch Learn about objects and behavior Programming motion and sound Programming user interaction Creating your own story, game, entertainment piece, or simulation (starting Wednesday) ITEC-I5 Scratch Aug 2009 20 PREFACE These slides are intended to be used in an active lab demo and discussion and are therefore not complete by themselves. Scratch has a nice facility for working with sounds; however, during the intro only the instructor’s computer should have speakers. When students get to individual work later, they can use headsets and microphones. ITEC-I5 Scratch Aug 2009 21 Simple ops first Sprites are objects We operate on their color, size, position We move them We have them say things ITEC-I5 Scratch Aug 2009 22 Click on the “Looks” button at the top left. ITEC-I5 Scratch Aug 2009 23 Major components At right: the stage with sprite[s] or objects or actors At left: operations and attributes for the sprites Center: scripts or program[s] for the behavior[s] of the sprites Your sprites are actors that you direct with your scripts ITEC-I5 Scratch Aug 2009 24 The “hello” script Can do it in 57 languages – java, C++, … Scratch Easy in Scratch: select “Looks” operations and drag the “hello operation” onto your center panel. Then double click on this “lego block”: check your sprite behavior at the right Your very first Scratch program! ITEC-I5 Scratch Aug 2009 25 Make the cat 50% larger 1. Select “Looks” operations 2. Drag the “change size” operator into your script 3. Click and edit for a 50% change (increase) 4. Double click your one operation script 5. Did your cat sprite get 50% bigger? ITEC-I5 Scratch Aug 2009 26 Putting a sprite in a location Motion ops X is + X is – Go to x , y Y is + Y is + Set x to Origin is (0, 0) Set y to X is – X is + Glide to Y is - Y is - ITEC-I5 Scratch Aug 2009 27 Your sprite’s “attitude” Try a “move op” to see changes. Try “rotation ops” as well. Choose “Motion” ops Click on “attitude variables” ITEC-I5 Scratch Aug 2009 28 Locating your sprite Interesting task: make your own “glide to” operation and have your sprite glide to (200, -100) ITEC-I5 Scratch Aug 2009 29 Scripting a sequence of ops Do ops in the following order by dragging operation blocks into a single connected block Say hello Move 200 steps forward Grow 50% bigger Make the “meow sound” ITEC-I5 Scratch Aug 2009 30 Result of 4 operation script ITEC-I5 Scratch Aug 2009 31 Some new operations •color change (Looks) • wait (Control) • move (Motion) ITEC-I5 Scratch Aug 2009 32 Exercise: write a script to Make the cat move along a square path Say “hi” at all four corners Wait 3 seconds at each corner Change color at all four corners Double size when back to the original starting location. Say “That’s all folks” when done. Show an instructor that you have achieved this. ITEC-I5 Scratch Aug 2009 33 Using variables Script might have to remember information How far is the cat from the dog? How fast is the rocket moving? Where did the user click on the stage? ITEC-I5 Scratch Aug 2009 34 Let’s implement an algorithm to average two numbers Make a variable “number1” (click and drag and set) Make another one “number2” ITEC-I5 Scratch Aug 2009 35 Compute average first as sum Make variable average Drag a “set operation” to script area Drag a + operation Drag variables number1 and number2 to parameters Click to execute ITEC-I5 Scratch Aug 2009 36 Average script as 4 operation sequence. Change the two numbers and click the sequence to execute the block again. ITEC-I5 Scratch Aug 2009 37 Elements of Scratch: objects Colors Sounds We want to use Scratch to program with Locations in 2D space multimedia. Sprites Costumes Variables (to remember the state of things) Events: that are broadcast for communication ITEC-I5 Scratch Aug 2009 38 Elements of Scratch: control Sequence of operations Loops or repetition Detecting events (key or mouse pressed, sprites overlapping each other, sprites hitting edge of stage, sensor giving value) ITEC-I5 Scratch Aug 2009 39 Loops are for repeating sequences Bethoven’s 5th: bump-bump-bam; bump-bump-bam; … Running the bases in baseball or driving around the block. Milling around waiting for some event to occur (in the aquarium example, the fish sprites mill around forever) ITEC-I5 Scratch Aug 2009 40 Loop constructs in Scratch Try these! Repeat N times Repeat forever Repeat forever if some condition exists (suppose I’m a sprite wandering about this lab until someone asks a question) ITEC-I5 Scratch Aug 2009 41 Exercise: use a loop to Move sprite around the 4 corners of the square Wait 2 seconds at each corner Say something at each corner Double size when done Change color when done Show an instructor that you have achieved this. ITEC-I5 Scratch Aug 2009 42 Play and examine MadLib Choose the “file” option at the top of the window Choose “open”, then “examples” Choose “stories” Choose “MadLib” and then read the authors instructions Click OK, wait for load, click green flag ITEC-I5 Scratch Aug 2009 43 About the MadLib story How many actors (sprites)? What is the role of the girl? How are the answers you give 'remembered' and then used in later actions? What is the role of the little whale? What makes the little whale flip around? What makes the big whale spout? ITEC-I5 Scratch Aug 2009 44 Tuesday: computing distances and directions (30 min) How to go from here (A) to there (B)? Computing distance Computing direction or heading How useful in Scratch or navigation, etc.? ITEC-I5 Scratch Aug 2009 45 Angles are important 180 degrees About 30 degrees (straight angle) About 45 215 deg degrees 90 degrees (right angle) 360 deg complete circle http://www.mathsisfun.com/geometry/degrees.html To see animation of angle measure. ITEC-I5 Scratch Aug 2009 46 Using a protractor to measure angles ITEC-I5 Scratch Aug 2009 47 Measure some angles with a protractor C Q P B A ITEC-I5 Scratch Aug 2009 48 The treasure is buried under an oak tree 42 degrees to the right of the line between the statue and post post 42 deg statue ITEC-I5 Scratch Aug 2009 49 Right triangles are special What is the distance B from point A to point B? Do this on graph paper. Draw the triangle ABC 3 with side CB = 3 and side CA = 4. Cut a “ruler” out of C A graph paper to measure 4 the side AB. ITEC-I5 Scratch Aug 2009 50 Measure another triangle C 12 B 5 A person walks north 5 miles from A to C A and then east 12 miles from C to B for a total of 17 miles. How far would the person walk going directly from A to B? (Do this on a scale drawing.) ITEC-I5 Scratch Aug 2009 51 Pythagorean theorem Long ago Pythagorus discovered a b that in a right triangle, with short sides a and b, the long c side c is such that c times c is hypotenuse equal to axa + bxb The scare crow said it in the cxc=axa+bxb Wizard of Oz: “In a right This is of great use in triangle, the square of the engineering and navigation. hypotenuse is equal to the sum of the squares of the other two sides”. ITEC-I5 Scratch Aug 2009 52 Shortest distance from A to B? C 25 B It’s 65 miles going north from 40 A to C and then east from C to B. What if we go the direct path from A to B along a A straight line? ITEC-I5 Scratch Aug 2009 53 Scratch script: distance A to B Pick point A with the mouse Pick point B with the mouse Compute the distance from A to B Test separately! ITEC-I5 Scratch Aug 2009 54 Test the first part separately We ask the user to click the mouse. We use variables Ax and Ay to save the mouse click position, then move our sprite there (156, 82) and change its color. ITEC-I5 Scratch Aug 2009 55 Test the second part (point B) After double clicking on our second code segment, our sprite has moved from A, where both x and y were positive, to B where both x and y are negative. Our variables are displayed. B = (-99,-51) ITEC-I5 Scratch Aug 2009 56 Test the final distance comp. Executing the above code, results in the stage at the right. Our sprite has moved a distance of 287.6 in going from point A to point B. (Extra: In what direction did it move?) ITEC-I5 Scratch Aug 2009 57 exercises Solve the distance Find a distance on problem by the earth using your changing the script actual GPS reading to not use mouse from your input. geocaching unit. Just set (Ax, Ay) to (0,0) and (Bx, By) to (25, 45) and execute! ITEC-I5 Scratch Aug 2009 58 Shortest distance from A to B? C 25 B Solve the distance problem by changing the script 40 How far to not use mouse A to B? input. Just set (Ax, Ay) to (0,0) and (Bx, By) to (25, 45) and A execute! ITEC-I5 Scratch Aug 2009 59 Using Octave to solve it (You can use a scale drawing too.) >> b = 40 % declare variable b to have value 40 miles b =40 >> a = 25 % declare variable a to have value 25 miles a =25 >> cSquared = a * a + b * b % compute the square of the hypotenuse (long side) cSquared =2225 >> c = sqrt(cSquared) % we need the square root of 2225 c = 47.1699 >> c * c % the square root times itself must be 2225 it is! ans =2225 % the direct route is about 47 and 1/6 miles; much less than 65 ITEC-I5 Scratch Aug 2009 60 Tuesday: Scratch more More about control in Scratch. How to control sprite behaviors? How to control user interactions? ITEC-I5 Scratch Aug 2009 61 Conditions can be checked Do something if sprite k hits sprite m Do something if a certain key is pressed Do something is some variable takes a certain value ITEC-I5 Scratch Aug 2009 62 Interacting with your sprite or story Using mouse Entering a character Asking the user a question ITEC-I5 Scratch Aug 2009 63 Sprite follows the mouse Try changing the number of steps or the wait time. ITEC-I5 Scratch Aug 2009 64 Sprites can interact with each other Can detect when colors overlap in space Can detect when sprites bump into edge of the stage Later: See “bouncing balls” example under Simulations under Examples Interact with this simulation Check out the rather complex scripts ITEC-I5 Scratch Aug 2009 65 Simple communicating sprites Dog talks to cat in “forever” (infinite) loop Dog sprite sends a message to the cat sprite Cat sprite says “hello” and gives the floor back to the dog ITEC-I5 Scratch Aug 2009 66 Cat sprite reacts to dog ITEC-I5 Scratch Aug 2009 67 exercises A) modify the above scripts so that a global variable is used to count how many times the dog says “Hello” B) change the control so that when “Hello” is said 10 times by the dog, the script stops with the dog saying “That’s all folks”. C) change the scripts so that each sprite moves to a random position on the stage before saying “Hello” Show your work to an instructor when you get finished with each part . ITEC-I5 Scratch Aug 2009 68 Check out the break dance example Open examples; music and dance; break dance How does break dancing begin? What are the roles of the sprites? What events are in the scripts? What should happen when the boom box is clicked? ITEC-I5 Scratch Aug 2009 69 Wednesday Goals Computing directions or headings in Scratch or Octave (30 min) Studying Scratch examples done by others (50 min). Design a project: story, game, simulation, or entertainment/art to do by Friday. (Sketch your plans in your journal and discuss with instructor.) ITEC-I5 Scratch Aug 2009 70 Wednesday: practical trig 1) Scale drawings 2) Angles and distances 3) Using trig functions ITEC-I5 Scratch Aug 2009 71 Heading from point A to point B Suppose my GPS (22, 10) * says I am at x=10; y=5 N My treasure is at x=22 and y=10 What is my heading ** E and how far do I (10, 5) travel? ITEC-I5 Scratch Aug 2009 72 Make a scale drawing and measure the angle and distance. ITEC-I5 Scratch Aug 2009 73 Tangent of an angle B Do you see THREE similar triangles? All share the vertex and angle A. Are there more? B2 30 B3 20 10 20 A C3 C2 C 60 ITEC-I5 Scratch Aug 2009 74 Tangent of an angle 10/20 = 0.5 = ½ B 20/40 = 0.5 = ½ 30/60 = 0.5 = ½ B2 15/30 = 0.5 = ½ where is this triangle? 30 5/10 = 0.5 = ½ where is this B3 20 triangle? 10 20 A C3 C2 C 60 ITEC-I5 Scratch Aug 2009 75 Tangent of an angle B If C2 is distance 47 from A, how long is side B2-C2? _____ B2 If B3-C3 has length 12, how long is A-C3 ? _______ 30 B3 12 A C3 C2 C 60 ITEC-I5 Scratch Aug 2009 76 Tangent of an angle is its RISE divided by its RUN Carpenters use the terms RISE and RUN to measure how Tangent of angle = steep a roof angle rise/run is. All roofs making the = “slope” rise same angle, have the same ratio RISE/RUN Size of the house run doesn’t matter! ITEC-I5 Scratch Aug 2009 77 Using the hypotenuse and one leg 10 more minutes and a few slides B needed to do this >> rise = 6 rise = 6 Hyp = 10 Rise >> hyp = 10 =6 hyp = 10 >> angleA = asind(rise/hyp) C A angleA = 36.8699 sin A = rise / hyp >> sind (36.8699) %in degree ans = 0.6000 ITEC-I5 Scratch Aug 2009 78 What’s the distance from A to C? Use the cosine to Use the Pythagorean compute it. Theorem to compute cosine A = run / hyp it. run = hyp * cosine A 10^2 = b^2 + 6^2 ITEC-I5 Scratch Aug 2009 79 Problem: angles and sides Draw any right triangle Measure one side Measure one angle What is the missing angle? ______ What are the missing sides? ____ ____ Check the Pythagorean relation ______ Check the sind and cosd relations ___ ___ ITEC-I5 Scratch Aug 2009 80 Angles in Octave >> rise = 20 rise =20 >> run = 40 run = 40 >> angle = atand(rise/run) % function or operator atand gives your angle in degrees angle = 26.5651 >> rise = 30 rise =30 >> angle = atand(rise/run) angle = 36.8699 ITEC-I5 Scratch Aug 2009 81 Angles in Scratch ITEC-I5 Scratch Aug 2009 82 Computing the angle Execute each of the 3 code segments. Slope is 0.5 or ½ The angle is about 27 degrees. ITEC-I5 Scratch Aug 2009 83 Heading from point A to point B Suppose my GPS (22, 10) * says I am at x=10; y=5 N My treasure is at x=22 and y=10 What is my heading ** E and how far do I (10, 5) travel? ITEC-I5 Scratch Aug 2009 84 Use atand to compute heading >> east = 22-10 % miles east = 12 >> north = 10-5 % miles north = 5 >> angle = atand(east/north) angle = 67.3801 % head 67 degrees east of north ITEC-I5 Scratch Aug 2009 85 Using a different triangle >> rise = 10-5 %miles rise = 5 >> run = 22-10 %miles run =12 >> angle = atand(rise/run) angle = 22.6199 % head about 23 degrees north of east ITEC-I5 Scratch Aug 2009 86 Exercises in computing angles A) Repeat the A above Octave 30 20 solutions in C Scratch 24 C B) Find the A 45 36 angles A at 50 the right (angle C=90) A C ITEC-I5 Scratch Aug 2009 87 Exercises in Scratch (50 min) Do some of the triangle exercises – any of them from geocaching? Study the aquarium program to see how the various fish behave; change fish color and observe the change; change its speed and observe; what other behavior changes can be made? Students study and modify existing Scratch programs; students imagine creating a program of their own. ITEC-I5 Scratch Aug 2009 88 Student Scratch project Pick a project: story, game, simulation, or entertainment/art to do by Friday. (Sketch your plans in your journal and discuss with instructor.) ITEC-I5 Scratch Aug 2009 89 Experiment with Scratch as time permits Thur and Fri Try your own scripts: make moves, sounds, interactions in simple cases Try the examples and learn what makes them work Download Scratch on your own machine and experiment some more Direct a story; or a simulation; or create a video game. ITEC-I5 Scratch Aug 2009 90

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