arrays.step

goals do
  goal "Make some arrays and do stuff with them"
  goal "Retrieve data from arrays"
end

step do
  irb <<-IRB
    fruits = ["kiwi", "strawberry", "plum"]
  IRB
  message 'An array is a list of things in square brackets, separated by commas.'
  message 'We generally call the individual things in an array **elements**.'
  irb <<-IRB
    things = [5, 'tree', 19.5]
    things.length
  IRB
  message 'An array can contain all sorts of things, not just strings.'
  message '`length` is a method that tells you how many **elements** are in an array.'
  irb <<-IRB
    empty_array = []
    empty_array.length
  IRB
  message 'The simplest kind of array is the empty array.'
end

step do
  irb <<-IRB
    fruits[0]
    fruits[1]
    fruits[2]
  IRB
  message 'Array elements are stored in order. You can retrieve them by using the square brackets to access them by their **index**.'
  message 'Arrays are ordered: elements remain in the same order they started in.'
  message 'Ruby starts counting at zero: the first element is `fruits[0]`.'
  irb <<-IRB
    fruits.first
    fruits.last
  IRB
  message 'Ruby gives us some helpful ways to get the first and last element from an array.'
end

step do
  irb "['salt'] + ['pepper']"
  message 'Arrays can be added together with the plus operator.'
  irb <<-IRB
    fruits + ['mango']
    fruits
  IRB
  message 'The plus operator doesn\'t modify the existing array, it makes a new one. How could you write that last piece of code to also modify the fruits array?'
end

step do
  irb <<-IRB
    fruits = ["kiwi", "strawberry", "plum"]
    fruits.push('apple')
    fruits.pop()
  IRB
  message 'Ruby has many methods for modifying arrays. What did these two methods do?'
end

explanation do
  message "Arrays are used whenever you need to work with a large group of similar items."
  message 'A short list of methods for Array:'
  table class: 'bordered' do
    tr do
      td 'length'
      td 'how long is this array (how many elements)'
    end
    tr do
      td 'first'
      td 'get the first element of the array (same as array[0])'
    end
    tr do
      td 'last'
      td 'get the last element of the array (same as array[-1])'
    end
    tr do
      td 'push'
      td 'add a new element to the end of the array'
    end
    tr do
      td 'pop'
      td 'remove (and return) the element at the end of the array'
    end
  end

  message "We are learning that different types of objects in ruby have different sets of methods. We can call `pop` on object of type `Array`, but we can't call it on an object of type `Float`."

  irb <<-IRB
    [].pop
    3.0.pop
  IRB

  message "In object oriented programming, each type of object shares a common list of methods. This list of methods is different for every type of object. When you attempt to call a method that is not available for the object's type, you get a `NoMethodError` and the interpreter stops running the program."
end

further_reading do
  a "Ruby's documentation for Array", href: 'http://www.ruby-doc.org/core-1.9.3/Array.html'
end

next_step 'hashes'