array_intro.md

Introduction to Arrays

Goals

Students should be able to:

• Explain what an array is
• Create an array and assign values to elements in the data structure
• Access specific elements through the index number.
• Iterate through an array.

Overview

Arrays are like a list of things. They maintain elements in order and identify each element with an index number. The first element is at index 0, the second at index 1, and so on.

list = ['Ada', 'Charles', 'Dee', 'Dan']

puts list[0] # Ada

puts list[1] # Charles

You can also access the last element in an Array with the index -1, and the 2nd to last with -2.

puts list[-1] # Dan
puts list[-2] # Dee

Arrays also have a method .length which returns the number of elements in the array.

puts list.length # 4

You can also use the length to find the index of the last element:

puts list[list.length - 1] # Dan

Question How can you find the 2nd to last element in any array without using -2?

Click here to see an answer:

puts list[list.length -2]

Looping Through an Array

You can also loop through an array with the array's .each method.
This code:

list = ['Ada', 'Charles', 'Dee', 'Dan']

list.each do |name|
  puts "Hello #{name}!"
end

Prints out:

Hello Ada!
Hello Charles!
Hello Dee!
Hello Dan!

The .each method will iterate through the array. On the 1st iteration name becomes "Ada", on the second iteration name becomes "Charles" and so on, until on the last iteration name will be set to "Dan".

Exercise

Fill in the missing code to calculate an average of the values in the list. Hint what data type should you use?

  list = [3, 5, 6, 15, 27]
  sum = 0

  # Your Code here



  puts "The average is #{average}"

Resources

• Array Documentation
• Ruby for Beginners - Arrays