Different Use of random() in Videos vs. Magic 8 Ball Project

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Leta

2018. február 12. 2:36

I've done several evaluations for the Magic 8 Ball project. I noticed that people seemed to be having trouble figuring out the range of values to expect from the call to random().

I believe that this is largely due to the fact that random() is never fully explained. Its use is demonstrated in one of the videos. But when it's used to produce (pseudo)random integers, the person in the video uses round(). So the example integer = round(random(1, 3)); produces values between 1 and 3 inclusive. However, when given the Magic 8 Ball Project immediately after this, the example code uses floor().

floor() is never introduced or explained anywhere. Neither is random() for that matter, beyond the fact that it will return random numbers between the two values passed to it. But the fact that it is between arg1 and arg2 exclusive (rather than inclusive) is never actually mentioned. I only know this because I have some previous experience with programming.

So, floor(random(1,5)) will return integer values between 1 and 4, not 1 and 5. But, since random() has never been fully explained and floor() has never even been mentioned, a lot of people working on this project assume that the values produced will include 5.

If floor() and random() aren't going to be fully explained and introduced before the Magic 8 Ball project, then I think it would make more sense to use round() in the example code to remain consistent with what students have already seen.

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Admiral Betasin

2018. február 12. 3:01

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I really agree with this. I have seen projects where the user simply removes the floor() command which leads to the mistake of them using > instead of ===

Thanks for your feedback!
Evan Lewis

2018. február 12. 3:48
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Hi Leta,

Thanks for your feedback!

I have also noticed frequent confusion amongst students trying to complete this project. This mostly comes from their lack of understanding of the floor() function.

Theoretically, floor(random(1, 5)) should never equal 5. However, sometimes it does due to a bug in ProcessingJS. I usually recommend that users use ifs and else ifs to check for the values 1 through 3, and then use an else statement to check for 4 and the very rare 5.

The reason why the project uses floor() instead of round() is that you're supposed to create a type of "fair die", where each message has an equal chance of being displayed.

When using round(), the random number is rounded to the nearest integer, but when using floor() the random number is always rounded down.

So if you use round(), the only way to get 1 is if the random number is less than 1.5 and greater than 1 (which is typically the min value). And the only way to get 2 is if the random number is greater than 1.5 and less than 2.4, a much greater range (practically speaking) than 1 to 1.5

With floor(), the result will be 1 if the random number is less than 2, and the result will be 2 if the random number is less than 3 but greater than 2. These ranges are both equal, and thus a "fair die" is created.

Unfortunately there's not a whole lot of documentation on random and its bugs, but there are several users who have published information about the bugs. You can find more information about non-user bugs on Inger's webpage: https://www.khanacademy.org/computer-programming/dgpe-non-user-bugs/6464050881822720

Let me know if you have any further questions!

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Different Use of random() in Videos vs. Magic 8 Ball Project

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