Compare remainder to 0 when checking for oddness

When checking whether a number is odd, always use x % 2 != 0 rather than the more common x % 2 == 1.

Note that, unlike most rules here, this one is not Scala specific.

Reason

There are odd numbers whose division by 2 has a remainder that’s not 1:

-3 % 2
// res0: Int = -1

The mathematical definition of odd and even numbers is:

• an even number is one whose division by 2 has no remainder
• an odd number is not even

This suggests the following implementations:

def isEven(i: Int): Boolean = i % 2 == 0

def isOdd(i: Int): Boolean = i % 2 != 0

And, indeed:

-3 % 2 != 0
// res1: Boolean = true

Checked by