Introduction to Computer Science with Scratch and App Inventor
Introduction to Computer Science with Scratch and App Inventor
Introduction to Computer Science with Scratch and App Inventor
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Look out for the duck!<br />
You might notice that if you s<strong>to</strong>p the<br />
game <strong>and</strong> then restart it, the variable<br />
points still has the same value. We<br />
probably want points <strong>to</strong> start over every<br />
time we restart our game. Giving a<br />
variable a starting value is called<br />
initialization.<br />
We can easily initialize our variable by<br />
adding code that sets it back <strong>to</strong> zero<br />
every time the green flag is clicked.<br />
So far, our dinosaur earns points by eating bowls of cheesy poofs. Let’s make things a little harder for<br />
the dinosaur. Our dinosaur is afraid of ducks, so let’s add a duck sprite that moves r<strong>and</strong>omly around<br />
the stage. The dinosaur must try <strong>to</strong> avoid the duck while he eats cheesy poofs. If the duck catches the<br />
dinosaur, the dinosaur loses two points.<br />
When we want <strong>to</strong> add a lot <strong>to</strong> our program all at once, it helps <strong>to</strong> break it down in<strong>to</strong> smaller steps.<br />
Then we can do one step at a time <strong>to</strong> make the programming easier. For example:<br />
1. Add a duck sprite<br />
2. Make the duck sprite move r<strong>and</strong>omly around the screen<br />
3. Have the duck sprite recognize when it is <strong>to</strong>uching the dinosaur<br />
4. When the duck <strong>to</strong>uches the dinosaur subtract two points from the dinosaur<br />
There are many different scripts you can write <strong>to</strong> create this program. Often in programming there is<br />
more than one way <strong>to</strong> do things. Also, you will notice that many of the steps <strong>to</strong> program our duck are<br />
very similar <strong>to</strong> steps we <strong>to</strong>ok <strong>to</strong> program the dinosaur <strong>and</strong> the poofs. This is also a characteristic of<br />
programming: lots of times you will only have <strong>to</strong> solve a problem once <strong>and</strong> you can reuse the solution.<br />
So, you can tell if the dinosaur is <strong>to</strong>uching the duck the same way you checked <strong>to</strong> see if the dinosaur was<br />
<strong>to</strong>uching the cheesy poofs!<br />
Here is a very simple duck program. Feel free <strong>to</strong> get creative!<br />
This part of the code makes the duck move<br />
around the screen<br />
This part of the code h<strong>and</strong>les what happens<br />
when the duck catches the dinosaur<br />
mbrace Game Development Workbook Page 24