A Virtual LOLcat in Scratch

Table of Contents

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1 Using functions

Learn It

  • Open up the Virtual_LOL_Cat script you were working on last lesson.
  • Functions are really important in coding.
  • A funtion is a named part of a program that performs some specific task
  • In Scratch, Functions are called Blocks.
  • Imagine I wanted you to make me a cheese sandwich. I could give you a set of instructions such as:
    • Take two pieces of bread.
    • Apply butter to one side of each piece
    • Place a slice of cheese on the butter side of one piece of bread.
    • Place the other slice of bread, butter-side down onto the cheese.
  • However, it's much easier to just say "Make me a cheese sandwich" as you probably already have the instructions stored in your memory. You have a named instruction for performing the sandwich making task
  • Functions allow us to write some code, and then run that code just by calling the name of the function.

Code It

  • Killing the pet is something we might want to do quite a lot. So it would make sense to create a Function for killing the pet, that we can use over and over again.
  • First we'll need to disconnect the code to kill the pet, from the when space key pressed event.

Function_1.png

  • Next we'll create a new function.
    1. Click on More Blocks
    2. Click on Make a Block
    3. Call it KillPet
    4. Click on OK

Function_2.png

  • A new define KillPet block should have been created. This is your named function that you can attach your code to.
  • Now we'll use the function
    1. Attach your code to kill the pet to the new define KillPet block.
    2. From More Blocks drag your KillPet block onto the Scripts Area
    3. Attach the KillPet block to the when space key pressed event

Function_3.png

Run It

  • Test your code to make sure it works like it did before. The pet should die when the space key is pressed.

2 Using variables

Learn It

  • Variables are another important concept in programming.
  • A variable is made up of two things:
    1. Some data that is stored (like numbers or letters)
    2. A name that links to that data.
  • You have variables stored in your memory, even though you might not have realised it.
  • If I ask you what your name is, you can tell me. Your name is a variable.
  • If I ask you what your age is, you can tell me. Your age is a variable.
  • A key thing to remember about variables, is that they can change. You could legally change your name to "Ima Coder", and your age increments by 1 every time you have a birthday.

Code It

Cookie_Cat.jpg

  • We're going to use a variable to represent how hungry our pet is.
  • The variable will have a name - PetHunger
  • The variable will store some data - 0 to represent no hunger, upto 100 to represent starving.
    1. Click on the Data palate
    2. Click on Make a variable
    3. Call it PetHunger
    4. Click OK

Variable_1.png

  • To finish off this section, you'll need to create a new script to handle the PetHunger.
  • Add a new when greenflag clicked event.
  • Attach a set PetHunger to 0 block beneath it. We'll add more to this part in the next lesson.

Try It

  • We're going to need some more variables for our virtual pet, so we might as well create them now.
  • Create variables to for PetTiredness, PetThirst and PetHappiness.
  • Each variable needs it's own when green flag clicked event.
  • PetTiredness should start at 0. PetThirst should also start at 0. PetHappiness should start at 100.

3 Using loops

Learn It

  • Loops are the third fundamental concept in porgramming to learn today.
  • A loop causes instructions to be repeated over and over again.
  • There are basically two types of loop
    • Loops that repeat a set number of times
    • Loops that repeat until a condition is met.
  • Imagine someone was giving directions. They might say something like;
At the next four roundabouts take the second exit to go straight on.
  • This is a loop that repeats four times. You take the second exit at each roundabout exactly 4 times.
  • They might have said this instead though;
Keep taking the second exit at the roundabouts, until you go under the blue bridge.
  • This loop repeats an unknown number of times, until the you go under the bridge.
  • In Scratch these types of loop are called the repeat and the repeat until loops.

Code It

  • We're going to use a repeat until to make our pet get hungry.
  • In Scratch you nest the code you want to repeat, insite the loop block.
  • Here's the complete script code. You build it from the script you already have to set the Pet's Hunger to 0
when green flag clicked
set PetHunger to 0
repeat until PetHunger = 100
    change PetHunger by 1
    wait 0.1 secs
KillPet
  • This code can be tricky to assemble, so if you want to see an image of the completed script, then click here, but have a go at doing it yourself first.

Run It

  • Run your script to make sure that it works.
  • You should see the PetHunger variable increase on the stage.
  • When it reaches 100, the pet should die.
  • If it doesn't work then go back over the instructions, then ask a friend and finally ask your teacher for help.
  • For testing purposes, we've used a wait period of 0.1 secomds. But this isn't really practical for the real Virtual Pet. Change the wait time to something longer. You can choose any value you like.

4 Badge It - Explaining it all

Badge It - Silver

  • Upload the script you have complete after following the notes above.

Badge It - Gold

  • Create a new Scratch file
  • In your new Scratch file, create scriptes where a character explains the concepts of Functions, Variables and Loops to someone who has never heard of the terms. Try to come up with your own examples.
  • For Gold badge, your animation explains the two of the definitions of variables, functions, and loops.

Badge It - Platinum

  • In addition to the above Gold, your animation explains all three concepts in good English AND with relevant examples clearly showing excellent understanding.