Negative random numbers

Question

I know how to generate numbers with Rails but I don't know how to generate negative numbers?

prng.rand(1..6) for random of [1, 2, 3, 4, 5, 6]

Random doc says that you would get an ArgumentError.

Answer 1

Let's say you want to generate a number between a and b you can always do that using this formula:

randomNum = (b-a)*prng.rand + a

So if you want a number between -8 and +7 for example then a=-8 and b=7 and your code would be

randomNum = (7-(-8))*prng.rand + (-8)

which is equivalent to

randomNum=15*prng.rand - 8

Answer 2

Suppose you want to generate negative numbers between -1 to -5

You can simply do this:

rand(-5..-1)

It will generate random numbers between -5 to -1