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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


  • Strings
  • name = "Gavin"
  • name.length
  • String interpolation
  • new_string = "My score is #{41 + 1}"
  • Numbers
  • score = 42
  • Arrays
  • 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)
  • person = { "name" => "Gavin Stark", "score" => 42, "favorite_color" => "blue" }
  • person["score"] (returns 42)
  • person["favorite_color"] (returns blue)
  • Returns nil if the key isn't there person["address"] returns nil
  • Values (and keys, though they are usually strings) can be comples
    • `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

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

    case name
    when "Gavin"
    puts "Instructor"
    when "Mark"
    puts "Instructor"
    when "Jason"
    puts "Instructor"
    when "Dania"
    puts "Ops"
    when "Holly"
    puts "Ops"
    when "Toni"
    puts "Campus Director"