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Intro to Ruby

Ruby files

  • Store our code in files that end in .rb
  • Run our code from the terminal via ruby filenamehere.rb
  • We can access an interactive console with the program irb

Variables and basic types


  • name = "Gavin"
  • name.length
  • String interpolation
    • new_string = "My score is #{41 + 1}"


  • score = 42


  • scores = [100, 98, 42, 65]

  • Indexing

    • scores[0] is the first thing in the array (100)
    • scores[1] is the second thing in the array (98)
  • Negative indexing

    • scores[-1] is the last thing in the array (65)
    • scores[-2] is the second to last thing in the array (42)
  • Returns nil if the index isn't there

    • scores[500] is nil
  • Methods

    • length gives you the length of the array
  • Can store mixed types

    • my_array = ["Gavin", 42, "Toni", 100]
    • array_with_arrays_inside = ["Gavin", 42, ["Toni", "Jason"], 100]

Hash (like a dictionary)

  • Declaring
    • person = { "name" => "Gavin Stark", "score" => 42, "favorite_color" => "blue" }
  • Accessing
    • person["score"] (returns 42)
    • person["favorite_color"] (returns blue)
  • Missing keys
    • Returns nil if the key isn't there person["address"] returns nil
  • Values (and keys, though they are usually strings) can be complex
    • person = { "name" => "Gavin Stark", "scores" => [100, 98, 42, 64] }
    • person["scores"] is [100, 98, 42, 64]
    • person["scores"][2] is 42 since person["scores"] is an array, and then we index the array at 2 to get the third element

Interacting with users

Printing values

  • puts outputs information without any formatting. Good for user output
  • p outputs information formatted for programmer friendliness. Good for debugging.
name = "Gavin"
puts name # Would output: Gavin
p name # Would output: "Gavin"
empty_string = ""
puts empty_string # Would output:
p empty_string # Would output: ""

Reading values

  • gets retrieves information from input (usually the terminal from the user typing)
  • However, it includes a newline character (the return key that ends a line)
  • We use chomp to remove it.
puts "What is your name?"
name_with_newline = gets
name = name_with_newline.chomp
# or
puts "What is your name?"
name = gets.chomp
# or
puts "What is your name?"
name = gets(chomp: true)

Control Flow

  • if statements
if name == "Gavin"
puts "The name was Gavin!"
puts "The name isn't Gavin"


  • loop / break
loop do
puts "Give me some input"
input = gets.chomp
if input == "done"
puts "You said #{input}"

Ruby Comments

  • Comments start with a # mark. With a bare #, anything that follows will be ignored by Ruby.


  • Organizing code
  • Placing a name on a set of steps or a way of doing something
  • Methods have a name, and optionally a set of inputs (arguments) and a return
  • Example:
# This method has no inputs or return
def say_hello
puts "Hello there!"
# This method has an input but no returns
def say_hello(name)
puts "Hello there #{name}!"
# This method has inputs and a return
def make_sentence(name, score)
return "The score for #{name} is #{score}"
  • Without a return keyword, a method returns the value of the last statement of the function.
# This method has inputs and a return
def make_sentence(name, score)
"The score for #{name} is #{score}"

More control flow

  • Conditionals

    • Are two things true (AND):
      • if score > 10 && score < 80
    • Are either of two things true (OR):
      • if score > 90 || name == "Gavin"
  • What if we are looking for a few options? For this, we have the case statement

    case color_name
    when "red"
    puts "#F00"
    when "green"
    puts "#0F0"
    when "blue"
    puts "#00F"
    when "black"
    puts "#000"
    when "white"
    puts "#FFF"