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CS Unplugged activity

Creature Sorting

About 30 minutesSoloPencil

Every time a program makes a decision, it’s asking a yes-or-no question. if the door is locked, if health is greater than zero, if the player pressed jump: underneath, every one of those questions is built from just three words: AND, OR, and NOT. Get comfortable with those three words on paper, and you’ll read (and debug) real code faster, because you won’t have to guess what a condition means. You’ll know.

AND, OR, NOT, in plain words

  • AND is true only when both sides are true. round AND has_hat means “this creature is round, and it also has a hat.” Miss either one and the whole thing is false.
  • OR is true when at least one side is true, including when both are. round OR has_hat is true for round creatures, hatted creatures, and creatures that are both. That last part trips people up: in everyday speech “or” sometimes means “one or the other, not both,” but in code it never does, unless you write it that way yourself.
  • NOT flips whatever comes right after it. NOT round is true for every creature that isn’t round. It doesn’t touch anything else in the expression, just the piece right next to it, unless parentheses say otherwise.

The creatures

Sixteen creatures, sixteen combinations of the four traits above. Every creature has a number so you can write down your answers without redrawing anything.

CC BY-NC-SA 4.0.