;use last bit method
isOdd = i & 1         ;isOdd is non-zero if i is odd
isEven = i & 1 ! 1    ;isEven is non-zero if i is even

;use modular method
isOdd = i % 2         ;isOdd is non-zero if i is odd
isEven = i % 2 ! 1    ;isEven is non-zero if i is even