What is the correct way to obtain (-1)^n?

Question

Many algorithms require to compute (-1)^n (both integer), usually as a factor in a series. That is, a factor that is -1 for odd n and 1 fo

Answer 1

Usually you don't actually calculate (-1)^n, instead you track the current sign (as a number being either -1 or 1) and flip it every operation (sign = -sign), do this as you handle your n in order and you will get the same result.

EDIT: Note that part of the reason I recommend this is because there is rarely actually semantic value is the representation (-1)^n it is merely a convenient method of flipping the sign between iterations.