Lesson4 Teachers Guide
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Lesson 4 - Variables - Teacher’s Guide
http://www.stencyl.com/teach/act4/
Objective
Introduce students to (local) variables and promote principles of good coding. Students
will learn the following concepts.
Outcome
Students will take an existing behavior and modify it, so that it can be more easily reused
across the game, thereby promoting good coding habits.
Lesson Plan (1 - 2 hours)
Discussion
20 minutes
Cover the topics under Discussion Notes (Page 2)
Present the topics. Pose questions at appropriate points and encourage
students to participate in the discussion.
Activity
40 minutes
Extend an existing game
Students will apply what they’ve just learned to add functionality to an
existing game.
Activity
60 minutes
Work on extra activities
Students will work on a more challenging set of activities in order to
demonstrate mastery of the concepts they’ve learned.
Note: Extra activities are optional but recommended.
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Discussion Notes
Topic 1: Attributes
In the prior lesson, we worked with Global Variables (Game Attributes), variables that can
be referenced and modified anywhere within a game.
In contrast, Local Variables (Attributes) only apply to specific Actors and Scenes.
In the example above, the attributes include Health, Shirt Color and Hero’s Name.
(Ignore
Actor, which is an internal reference and best left out of this discussion)
Discussion: What’s the benefit of a local variable?
Answer: Suppose that local variables did not exist. If we only had global variables, how would we be able
to have variables corresponding to specific actors? If we don’t know ahead of time what actors will
participate, it becomes virtually impossible (or at best, inconvenient) to have enough global variables to
account for this.
Topic 2: Demonstrate how to work with Attributes
We recommend briefly showing students how to create an attribute (number or text),
using the blocks corresponding to that attribute and showing how the attributes show up
as configurable fields when a behavior is attached to an Actor or Scene.
TODO: Flesh this out into an explicit demo.
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Topic 3: Good Coding Habits
Code Reuse
Discussion: What happens if you have a feature that you want every enemy in a game to share? Should
you remake it for every enemy, or is there a better way?
Answer: That’s what behaviors are for.
Behaviors let you reuse functionality across an entire game (and by extension, across
multiple projects). That complex Jump behavior only has to be written once. This ability to
reuse a feature is the principle of Code Reuse.
Writing things once is a good thing. If you discover a bug, you just have to fix it one place,
versus several.
No Magic Numbers
Magic Numbers are unexplained numbers used in code. Generally speaking, if the number
isn’t 0, 1 or 2, it’s a Magic Number. It’s almost certainly a Magic Number if you use that
same number multiple times in the same behavior.
Magic Numbers are tempting to use because they are easy to type in and forget. But over
time, they can build up and make your code more difficult to maintain.
Attributes are the solution to Magic Numbers. They solve the problem in two ways.
●Attributes force you to come up with a name for the value, so the use of the value
becomes self-documenting.
●If you decide to change the value, for whatever reason, you change it one place,
versus several. Forgetting to change things that happen in multiple places is one of
the most common sources for bugs.
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