Exercise summary

Here are some things you learnt in the last exercise:

Accessing elements

• Arrays start from 0, so that the first elements is a[0]
• Arrays also allow indexing from the back, giving the last element as a[-1]
• If try to access beyond the end of the array it gives nil (instead of an error in other languages)
• You can access multiple elements by specifying a range, e.g. a[1..-1] is everything but the first element

Array methods

Arrays have many useful (and largely self-explanatory) methods, including:

• empty? - does the array have any elements, or is it the empty array []
• length
• include?(x) - is x in the array
• reverse, reverse! - as with strings the ! permanenty changes the array

Adding to an array

• You can add to an array by setting a given element explicitly a[5] = 6

• If the array isn’t long enough the gaps are filled with nil:

  a = [1, 2]
  a[6] = 5
  a #=> [1, 2, nil, nil, nil, nil, 5]
  

• You can also add to the end of an array by doing a << 5. This is very ‘rubyish’ and you’ll see it a lot.

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