arr = [1, 2, 3]

str = [1, 2, 3].to_s

arr = [15, 32, 13]
num = arr[2] # 13

arr = [1, 2, 3]
last_value = arr.pop # last_value: 3, arr: [1, 2]

arr = [1, 2, 3]
arr.push(4) # [1, 2, 3, 4]

arr = [1, 2, 3]
arr << 5 # [1, 2, 3, 5]

arr = [1, 2, 3]
result = arr.include?(1) # true

arr1 = [1, 2, 3]
arr2 = [1, 2, 3]

result = arr1 == arr2 # true

arr = [1, 2, 3]
arr.each do |item|
  # 3回実行され、itemの値は1, 2, 3と順番に変わる
  speak("ループ(each): #{item}")
end

arr = [1, 2, 3]
generated_arr = arr.map do |item|
  item * 2
end

# generated_arr: [2, 4, 6]

arr = [1, 5, 3, 2 ,3]
result = arr.find do |item|
  item == 2
end

# result: 2

arr = [1, 2, 3, 4, 5, 6, 7, 8]
result = arr.find_all do |item|
  # 2で割り切れる
  item % 2 == 0
end

# result: [2, 4, 6, 8]

arr = [3, 4, 1, 2]
sorted_arr = arr.sort # [1, 2, 3, 4]

arr = [3, 4, 1, 2, 5]
sorted_arr = arr.sort do |a, b|
  b <=> a
end

# sorted_arr: [5, 4, 3, 2, 1]