Ruby: Multiply all elements of an array

This is the textbook case for inject (also called reduce)

[1, 2, 3, 4, 5].inject(:*)

As suggested below, to avoid a zero,

[1, 2, 3, 4, 5].reject(&:zero?).inject(:*)

There is also another way to calculate this factorial! Should you want to, you can define whatever your last number is as n.

In this case, n=5.

From there, it would go something like this:

(1..num).inject(:*)

This will give you 120. Also, .reduce() works the same way.