An Introduction to the Ruby Language

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

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)

• 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!"
else
  puts "The name isn't Gavin"
end

Looping

• loop / break

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

Ruby Comments

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

Methods

• 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!"
end
# This method has an input but no returns
def say_hello(name)
  puts "Hello there #{name}!"
end
# This method has inputs and a return
def make_sentence(name, score)
  return "The score for #{name} is #{score}"
end

• 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}"
end

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"
  end