Task

Test whether an integer is even or odd.

There is more than one way to solve this task:

 Use the even and odd predicates, if the language provides them.
 Check the least significant digit. With binary integers, i bitwise-and 1 equals 0 iff i is even, or equals 1 iff i is odd.
 Divide i by 2. The remainder equals 0 iff i is even. The remainder equals +1 or -1 iff i is odd.
 Use modular congruences:
 i ≡ 0 (mod 2) iff i is even.
 i ≡ 1 (mod 2) iff i is odd.


(require 'cl-lib)
 
(defun even-or-odd-p (n)
  (if (cl-evenp n) 'even 'odd))
 
(defun even-or-odd-p (n)
 (if (zerop (% n 2)) 'even 'odd))
 
(message "%d is %s" 3 (even-or-oddp 3))
(message "%d is %s" 2 (even-or-oddp 2))