Introduction to Computer Science with Scratch and App Inventor

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