Why do you floor() + 1 instead of ceil() the Math.random() value?

Hi Edouard,

Consider the following example:

var num = Math.ceil( Math.random() * 4 );

After the code executes, num will be equal to 1, 2, 3, or 4. However, there is a very slight chance that the function Math.random() will return a value of 0. If that happens, then num will be equal to 0. This could cause an error in your program because a fifth random number (zero) may be generated, even though you intended to create only four random numbers.

You could use Math.ceil( Math.random() * 5 ) + 1 as well as Math.floor( Math.random() * 6 ) + 1

Thanks guys!

Will Math.ceil( Math.random() * 6 ) + 1 return 7 if Math.random() returns 1? I mean isn't the possibility to recieve 1 as a return value from Math.random() as great as recieving 0?

Is the answer that - both Math.ceil and Math.floor may return a zero, but you are able to add +1 to Math.floor to remain in the allocated guessing frame whereas adding +1 to Math.ceil may increase the number to beyond guessing frame? And the workaround would be multiplying Math.random by one less than the upper number if using Math.ceil and then adding one?

Found the answer: https://www.codecademy.com/forum_questions/4f977513839b6d0003005464

Using the upper - 1 workaround with ceil: "In this case, the range of values that maps to each output is different. In particular, the chance of getting a 0 (i.e. rolling a 1) is very tiny."

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.

From my understanding, there is no difference of using either or.

Math.floor() + 1 does the same thing Math.ceil() will do.

I hope this helps.