IsEven

isEven is a predicate that returns true if its input is an even integer, and false otherwise. In mathematics, an even number is any integer that can be written as 2k for some integer k. Equivalently, n is even when n mod 2 equals 0.

Parity theory notes that even numbers are closed under addition and subtraction; the sum or difference of two even numbers is even, while the sum of an even and an odd number is odd. The product of any integer with an even number is even.

In programming, isEven commonly tests divisibility by 2. Typical implementations use the remainder operator: n % 2 == 0. Some performance-sensitive code uses a bitwise check such as (n & 1) == 0 on two's complement integers. In many languages, these tests expect an integer input; passing a floating-point or non-numeric value may raise an error or yield false.

Edge cases include negative numbers, for which -4 is even because -4 = 2 * (-2). The concept extends to zero, which is even. Some languages define modulo with negative operands differently; checking for remainder equal to zero remains reliable in most cases.

See also parity, odd numbers, divisibility.