Ranges & capstone

1..5 vs 1...5 — inclusive vs. exclusive

A range is a compact way to describe "every value from here to there." Two dots include the end; three dots exclude it:

(1..5).to_a     # [1, 2, 3, 4, 5] — end INCLUDED
(1...5).to_a    # [1, 2, 3, 4]    — end EXCLUDED

.to_a turns a range into a real array. Ranges aren't just for numbers, either — to_a is just the easiest way to see one's contents while you're learning.