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Max Primo
976 PointsSo I was testing out the Math.ceil and Math.floor. But I never got 0 when I used Math.ceil. Mistake in the video?
So in the video it states that Math.ceil is not a good way to get a random number between 1-6 because you might end up with a zero. However, when I ran Math.ceil(Math.random()*6); I actually never got any zeros and they were all between 1-6.. Is this a mistake in the video? I am just confused. However, I did get 0 when I ran Math.floor(Math.random()*6); without adding the 1. But my point is that you can get 1-6 without adding the +1 if you just did Math.ceil?
3 Answers
Cameron Childres
11,818 PointsHey Max~
This is not an error, there's just an incredibly small chance to receive a zero value.
When you run Math.random() you get a random number in a range that starts with 0 and approaches, but never reaches, 1. I just ran Math.random() a few times in my browser, here are some results:
- 0.06402171468849871
- 0.0485511979040667
- 0.381454323282967
- 0.2018132157678454
Running Math.ceil() on any of these numbers will return 1, since it always rounds a number up to the next largest integer. Now take for example this number:
- 0.00000000000000001
This will also be brought up to 1 with Math.ceil() -- it's the next largest integer.
You'd get zero if the random number generated was precisely zero:
- 0.0000000000000000
There's something like a one-in-one-hundred-thousand-million-million chance of this happening, I wouldn't expect you to see it in a quick test -- BUT, it is possible.
Alasdair Glenday
4,394 PointsThanks so much Max and Cameron for this! Had me so confused as I was doing the exact same thing.
I understand now, that because Math.random makes a number between 0 and up to but not including 1, there's an incredibly small chance the random number might be 0.0000000000, which even multiplied by 6 and rounded up still equals 0.
Thank you both!
Michael Jacoby
Full Stack JavaScript Techdegree Student 3,793 Pointsconsole.log(Math.round(Math.random() * 6)) did return a 0. I didn't try it with a +1, because I thought it might return a 7.
Seems JS could have been a bit more user-friendly with randomDieRoll() or copy Python with randint and randrange.
Max Primo
976 PointsMax Primo
976 PointsOh I see, thank you for clarifying!
Charlie Bird
7,277 PointsCharlie Bird
7,277 PointsCame here to ask the same question. Thanks for explaining!