nums = [2,4,3,1,2]
sorted = nums.sort # returns a new sorted array. 'nums' is unchanged
p sorted #=> [1, 2, 2, 3, 4]
p nums #=> [2, 4, 3, 1, 2]
nums.sort! # sort 'nums' "in-place"
p nums #=> [1, 2, 2, 3, 4]