Before moving onto this video,
you should have added a backdrop
and two sprites to your project.
If you haven't done that yet,
please pause this video and do so now.
In this video you will learn how
to program the chaser sprite to start moving
in a random direction and bounce off the walls forever.
When computer scientists have large
or difficult problems to solve,
they use something called problem decomposition
to make solving the problem easier.
Problem decomposition means breaking a bigger
problem up into smaller steps.
To make this sprite point in a random direction
and bounce off the walls forever,
you'll break this problem into smaller steps.
One, move the sprite.
Two, move the sprite forever.
Three, make the sprite bounce off,
if it's on an edge.
And four, point the sprite in a
random direction when it starts.
First, move the chaser sprite.
Click the chaser sprite and drag on a move block.
Next, program the sprite to keep moving forward.
Click control and place a forever block
around the move block.
Click the block stack to test.
Awesome, the sprite keeps moving forward.
Next program the sprite to bounce
off the edges of the stage.
Click motion and drag the if on edge, bounce block
into your forever loop.
Try it by clicking on the forever loop.
Good, the sprite is bouncing back and forth on the stage.
The wouldn't be a very fun game
if the sprite only bounced back and forth like this.
To fix this, turn the sprite a random
amount of degrees at the beginning of the game.
This is a problem that you can break
down into smaller pieces.
To get a sprite to move a random amount,
you'll need it to turn first.
Drag out a turn block from the motion menu
and put it at the start of the program.
Each time the game runs down,
the sprite will turn 15 degrees
before starting to move forward.
From the operator's menu,
select a pick random block
and place it inside the turn block.
Set the values in the pick random
block to whatever you want.
Each time this block is read,
the computer will choose a random number
between the values you selected
and turn that sprite that amount.
Test your code.
Now tell the computer when to run this code.
Add a when flag clicked event.
Now it's your turn.
Program your chaser sprite to point
in a random direction, move forward forever,
and bounce of the edges of stage.
You might break down the problem into these steps.
Move forward, move forward forever,
bounce, if on edge, and turn a random direction
at the beginning of the game.
Finally, use a when flag clicked event
to start the game.
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