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JavaScript JavaScript Basics (Retired) Working With Numbers Create a random number

Ignacio Van Humbeeck
Ignacio Van Humbeeck
2,150 Points

Why not simply use Math.round? I test it and it also gives me 6 sometimes

Math.round( Math.random() * 6);

2 Answers

The answer is basically the same as why not use Math.ceil():

As the transcript says: Now you might be wondering why we don't just use the Math.ceil method. 4:45 It rounds upwards, so a number over five would round up to six. 4:50 It seems like a good idea, and might make it so that we don't have to 4:53 add one at the end of the statement to produce a number from one to six. 4:58 Unfortunately, there's a slight chance you'll end up with a zero. 5:02 Remember, the Math.random method returns a number from zero up to one. 5:10 The random number can actually be zero. 5:12 In this case using Math.ceil on zero returns zero. 5:18 So, if we did use Math.ceil, we could end up with numbers from zero up to and 5:23 including six.

There would be an equally slight chance that Math.round() could also yield a zero.
Julie Kohler
Julie Kohler
6,122 Points

Thank you, jcorum! That confused me as well.

Dennis Amiel Domingo
Dennis Amiel Domingo
15,577 Points

I'm a noob so pardon if my interpretation isn't correct. I guess the reason Math.ceil() is not advisable to use for a 6-dice roll is because there is a chance that it will return a 7? For example, if Math.random gives us 5.1, then that will be 6 right? Now when you perform the Math.ceil(5.1) + 1, that would give you 7, and 7 is not included in a 6-dice roll. Also, even if you get a 0 from Math.ceil, remember that it will be added to 1 right, so a Math.ceil(0) + 1 will give you 1, which is still inside the 6-dice roll.

I tried Math.ceil(Math.random() * 6) + 1; and it always gives me rolls between 2 and 7.

So to keep it simple, Math.ceil gives you a dice roll range of 2 to 7.

Hope that helps.

Peter Retvari
Peter Retvari
2,566 Points

I believe it's all about add 1 to the random number function, cause without this it could be end up with zero. and after we added 1 we have to use the floor function as well. Am I right?