1 an intro to programming concepts with scratch session 3 of 10 sessions repetition and variations
Post on 17-Dec-2015
214 Views
Preview:
TRANSCRIPT
1
An intro to programming concepts with Scratch
Session 3of 10 sessionsRepetition and
variations
2
Session 3 goals
• Learn how to program with repetition• Changing costumes • Controlling execution (behavior) using
special keys
3
The sneezing cat script
• We repeat 20 times
Say “AAAHHHH” for a short time Then grow the cat 5% bigger
4
Exercise: bring the cat size down to normal
Repeat 20? times Briefly say “CCHHEEEW” Then shrink the cat’s size by 5%
Repeat N times and repeat forever are in the Control menu
5
Program to compute the average
An optional piece: to omit this, proceed to slide #18
6
A better average algorithm ( do blackboard work first)
• Let’s average N numbers• Say 5 numbers { 12, 14, 15, 10, 10}• Variable sum will be used to add them• After we add all the numbers, we then
divide by N• In the example above, sum =0, 12, 26, 41,
51, and finally 61• Then average = 61/5 = 12.2
7
Exercise at your seat with paper
• Write SUM = 0• Write N = ____• Repeat with the class get the NEXT number __ __ __ __ __ add it to the SUM __ __ __ __ __• Compute the average by dividing the sum by N _____
8
Doing it in a Scratch program
• Ask the user how many numbers (N)• Set our SUM to 0• Repeat the following N times ask the user for the NEXT number reset SUM to SUM + NEXT• Set AVERAGE to SUM / N• Tell the user the AVERAGE
9
Making the script
• We need variables N, SUM, and NEXT• We need a repeat N loop• We need to ask the user for a number NEXT
inside the repeat loop• We need to add NEXT to SUM each time• We need to say the answer
10
AVG : making the variables
Make variables for:
N: how many to average
NEXT: the next number
SUM: the sum of the
numbers
AVERAGE: the average
of the numbers
11
AVG : asking for the numbers
Try this loop first and watchTry this loop; watch the value of NEXT change with your input.
12
Let’s write the program in 3 steps, and slowly execute it
Step 1: get NStep 2: ask the N numbers and add them
upStep 3: compute and say the average
13
AVG 1: get N from user
3 parts of our program: (1) ask user for N; (2) add up the N numbers; (3) compute and say the average. Click on each part to see it run!
14
AVG 2: add N numbers to SUM
We just added 12 and 14 and are ready to add 15.
We added 12 and 14 to sum and are asking for 15.
15
AVG 3: execute the 3rd part
Check all the variables to see if they are correct for this problem
16
Exercise: make a single script and run it on new numbers
17
Save your average program
You can always use it again in the future. That is what programs are for.
So, file it.
18
Exercise: have the cat do a flip by rotating 20 degrees 18 times.
• Repeat from the Control menu: set the number of repetitions to 18
• Rotate from the Motion menu: set the size of each small rotation to 20 degrees
19
Changing costumes
Another way to change the appearance of a sprite.
20
Making a new costume
1) Get bat2-a sprite from the “sprite box”.
2) Click on sprite
3) Click on “Costumes”
4) Click on “Import”
5) Now get bat-2b sprite from the sprite box
21
Use a loop to make the bat fly!
1) When and repeat from Control menu and 2) next costume from Looks menu.
22
Changing coordinates
• We can randomly set the location of the bat so it will “flutter”.
• Set X to a random number• Set Y to a random number• Move the bat to location (X,Y)• Of course, the bat should remain on stage!
23
Using pick random
Click the stop sign at the stage upper right to stop the forever loop.
Do we need a wait in the loop? Try it to see the change in flying.
24
Controlling the bat’s direction
• Let’s create multiple scripts.• Click space bar for random moves• Click right arrow to move right• Click left arrow to move left• The bat will behave differently depending
upon which key is typed!• (So, could a gamer catch the bat?)
25
Multiple interactive bat flight
26
Exercise:
• Add a behavior (script) to move the bat up with the up arrow.
• Add a behavior to move the bat down with the down arrow.
27
Adding a background
• Click on the Stage icon at lower right
• Click on Backgrounds
• Click on bat icon (Sprite1)
• Click on Scripts• FLY AGAIN!
28
Changing background
• Click on the stage icon• New menu of operations appears• Click each menu operation to see what it does.• How can we program changes of background?• More later.
29
Exercise: can we make Cassie do jumping jacks?
• Search the sprite locker to find different costumes for Cassie.
• Make a script that makes her move by contolling the changes in costumes.
30
End of Session 3: outcomes
Student should be able to write a program controlled by a loop, and execute a script by clicking special keys. The student should also know how to use “costumes” to change the
appearance of a sprite.
top related