Computational Thinking - Explode after 2 seconds

Now that we have learned the basics, we are starting to apply more sophisticated reasoning. The first task that we will consider is making some action last for 5 seconds.

Although time cannot be used to say how long a character does an action, time CAN be used to say how long a Boolean attribute is true for a character. So while you CANNOT say "The fox chases the rabbit for 5 seconds," you CAN say "When the fox touches a rock, the fox becomes empowered for 5 seconds." Then you can add, "When the fox is empowered, the fox chases the rabbit." You are basically saying the fox chases the rabbit for 5 seconds, but you specify when the 5 seconds of chasing happen.

The following game plan example will show you step by step how to make something explode 2 seconds after being shot. Since we cannot set a time for a Boolean attribute (death) to be false, we have to use a compound condition (more than one condition):

To illustrate this better, we can use color to help us as well.

When an alien is shot, it turns white for 2 seconds.	Just like the earlier example with the foxes, we give shot aliens a Boolean attribute (white) to be true for a certain amount of time '2 seconds'.
When an alien is shot, it turns white for 2 seconds. When an alien is shot, it becomes ready_to_explode.	The problem is, when those 2 seconds are up and the shot aliens return back to normal, there is nothing to tell them apart from the other aliens. So, we give the shot aliens a new attribute: 'ready_to_explode'.
When an alien is shot, it turns white for 2 seconds. When an alien is shot, it becomes ready_to_explode. When an alien is ready_to_explode and the alien is not white, it explodes.	The third sentence states the compound condition, which can only be met two seconds after being shot. The alien explodes when the attribute 'ready_to_explode' is true AND when the color attribute 'white' is false. After 2 seconds of being shot, the alien will satisfy the compound condition in the third sentence above. Do you see it?

Note that compound conditions joined by 'or' (such as "When the fox touches a rock or the fox touches a brick, ...") should be broken into two separate sentences:

When the fox touches a rock, ...
When the fox touches a brick, ...

Try it yourself: How would you make the alien explode after 3 seconds, but it does not change color at all?

Would the following work? Try it and see:

When an alien is shot, it becomes oh_oh for 2 seconds.
When an alien is shot, it becomes ready_to_explode.
When an alien is ready_to_explode and the alien is not oh_oh, it explodes.

Complete Sample Games for Explode after 2 seconds

// Game #1. Star Explosion.

// Game #2. Pearl Explosion.

// Game #3. Kill the Cobra Boss -- wrap around through the top border.

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