형태1
arr = [] # []
형태2
arr = Array.new # []
arr = [nil, nil ,nil] # [nil, nil, nil]
arr = Array.new(5) # [nil, nil, nil]
arr = Array.new(3, "ruby") # ["ruby", "ruby", "ruby"]
arr = Array(0...10) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]