Generate Random Whole Numbers within a Range

We can use a certain mathematical expression to get a random number between two numbers.

Math.floor(Math.random() * (max - min + 1)) + min

See Also: Explanation | Explanation in SO

Explanation

Math.random() creates a floating point number between 0 (inclusive) and 1 (exclusive)

Q: Create a random whole number between 2 (inclusive, min) and 6 (inclusive, max) i.e. create a random whole number between min (inclusive) and max (inclusive)

A: Math.floor(Math.random() * (6 - 2 + 1)) + 2

Let's write Math.random() * max which creates a floating point number between 0 (inclusive) and max (exclusive).

E.g. Math.random() * 6 generates a random floating point number between 0 (inclusive) and 6 (exclusive).

But we need to generate a whole number between 0 (inclusive) and max (inclusive) first. So we do a trick .

What if we create a number between 0 and max + 1. That way, we also include the max number. And then apply the Math.floor method on the result to get a whole number between 0 (inclusive, min) and max (inclusive).

We can write it as Math.floor(Math.random() * (max + 1)).

E.g. Math.floor(Math.random() * (6 + 1)) generates a random floating point number between 0 (inclusive, min) and 6 (inclusive, max).

0 1 2 3 4 5 6

The Math.random() * (6 + 1) part generates a floating point number between 0 (inclusive) and 7 (exclusive).

0..1..2..3..4..5..6..

But that doesn't solve our given question yet . We need to generate a random whole number between min (inclusive) and max (inclusive). So we need another trick .

What if we write Math.floor(Math.random() * ((max + 1) - min)) that will generate a whole number between 0 and (max + 1) - min.

E.g. Math.floor(Math.random() * ((6 + 1) - 2)) = Math.floor(Math.random() * 5) that will generate a whole number between 0 (inclusive) and 4 (inclusive).

0 1 2 3 4

But still the question is unsolved . We need the random number between min (inclusive) and max (inclusive).

So we simply write Math.floor(Math.random() * ((max + 1) - min)) + min .

E.g. Math.floor(Math.random() * ((6 + 1) - 2)) + 2 = Math.floor(Math.random() * 5) + 2

2 3 4 5 6

Now this answers our given question. Math.floor(Math.random() * (max - min + 1) + min correctly generates a random number between min (inclusive) and max (inclusive) i.e. it generates a random whole number between 2 (inclusive) and 6 (inclusive).