Ruby 101

Ruby is a dynamic programming language with a focus on simplicity and productivity. It has an elegant syntax that is natural to read and easy to write.

How to run Ruby code

1. In IRB

   You can run irb in the terminal to launch a Ruby interpreter. You can see it as a playground to test things out.

2. Using Ruby files

   Using Ruby files, for example wagon.rb. Launch your Ruby script from the terminal with:

   ruby path/to/your/file.rb

Built-in Ruby Objects

Everything in Ruby is an object. Objects have built-in methods you can call on them.

Strings

• To represent text
• Defined with single quotes or double quotes: 'wagon' or "wagon"

"wagon".class        # => String
"wagon".upcase       # => "WAGON"
"wagon".capitalize   # => "Wagon"

• You can inject Ruby code into a string using interpolation, but only in double-quoted strings

'two: #{1 + 1}'      # => "two: #{1 + 1}"
"two: #{1 + 1}"      # => "two: 2"

• You can convert strings to numbers

'1984'.class         # => String
'1984'.to_i          # => 1984
'1984'.to_i.class    # => Integer

• You can convert strings to arrays

'Change your life and learn to code'.class         # => String
'Change your life and learn to code'.split         # => ['Change', 'your', 'life', 'and', 'learn', 'to', 'code']

Integers

• To represent integers
• Can do standard arithmetic

4.class              # => Integer
1 + 2                # => 3
2 * 4                # => 8
4 / 2                # => 2

• Also has custom methods built-in

20.even?             # => true
20.odd?              # => false

• You can convert numbers to strings

1984.to_s          # => "1984"

Floats

• To represent decimal numbers

3.14.class         # => Float
1.23 + 2.1         # => 3.33

• Has it's own built-in methods

3.14.round         # => 3

Arrays

• To represent a list of elements, usually of the same type
• Defined with square brackets around the list of items

["paris", "london", "new york"].class     # => Array
[2, 5, 8, 2].class                        # => Array

• Has it's own built-in methods

["paris", "london", "new york"].length    # => 3
["paris", "london", "new york"].sort      # => ["london", "new york", "paris"]
[3, 5, 1].sort                            # => [1, 3, 5]

• You can convert strings to arrays

'Change your life and learn to code'.class         # => String
'Change your life and learn to code'.split         # => ['Change', 'your', 'life', 'and', 'learn', 'to', 'code']

• You access elements in an array based on its index, careful, indexes start at 0

beatles = ["john", "paul", "george", "ringo"]

beatles[0]         # => "john"
beatles[2]         # => "george"

• You add an element to an array by appending it or inserting it at a given index

beatles = ["john", "paul", "george"]

beatles << "ringo"
p beatles          # => ["john", "paul", "george", "ringo"]

• You modify an element in an array using its index again

beatles = ["john", "alex", "george", "ringo"]

beatles[1] = "paul"
p beatles          # => ["john", "paul", "george", "ringo"]

• You delete an element from an array by using its index or by using its value

beatles = ["john", "paul", "alex", "george", "arthur", "ringo"]

beatles.delete_at(2)
beatles.delete("arthur")
p beatles          # => ["john", "paul", "george", "ringo"]

Booleans

• To represent something that is true or false

DOCUMENTATION

The built-in methods are well-documented, don't reinvent the wheel...

• String methods
• Fixnum methods
• Floats methods
• Array methods
• Enumerable methods

Variables

• Allows you to store values to reuse them later
• You assign a value to a variable
• Variables can be overwritten and incremented

age = 21
puts "You are #{age} years old"

age = age + 1
puts "You are now #{age}"

first_name = "Alex"
last_name = "Benoit"

puts "My name is #{first_name} #{last_name}"

• By convention, variable names should be in snake_case (lowercase with underscores)

Methods

• Concise way to call Ruby code multiple times
• Apply the ruby code to dynamic inputs
• Defined with parameters and called with arguments
• A method always returns a result, and you can then operate on what is returned

def full_name(first_name, last_name)
  name = "#{first_name.capitalize} #{last_name.capitalize}"
  return name
end

puts full_name("boris", "paillard")

• In the example above, first_name and last_name were parameters and "boris" and "paillard" were the arguments, and we puts what returned from the method call
• We can call the method with variables too

my_first_name = "alex"
my_last_name = "benoit"
puts full_name(my_first_name, my_last_name)

• By convention, method names should be in snake_case (lowercase with underscores)
• By convention, methods ending with ? such as even? and start_with? return a Boolean

Flow Control

Conditionals and loops change the flow of a Ruby program. Conditionals allow us to execute a certain chunk of code under a specific condition. Loops allow us to execute a chunk of code multiple times. When the program is run, the code is executed from top to bottom, line by line, which is how you should debug in your head.

Conditionals (If/Unless)

If

If conditionals allow us to execute a certain chunk of code if a condition is "thruthy".

if condition
  # code executed only when condition is "truthy"
end

If/Else

If/Else conditionals allow us to execute a certain chunk of code if a condition is "thruthy" or another chunk of code if the same condition is not "truthy".

if condition
  # code executed only when condition is "truthy"
else
  # code executed only when condition is not "truthy"
end

For example, a small Ruby program that checks if you are old enough to vote:

puts "How old are you?"
age = gets.chomp.to_i

if age >= 18
  puts "You can vote!"
else
  puts "You cannot vote!"
end

Simple loops

While

While loops allow us to execute a chunk of code multiple times while a condition is "truthy".

while condition
  # executed while condition is truthy
end

For example, a small Ruby program that replicates the 'Price is Right' game.

price_to_find = rand(1..5)
choice = 0 # or `nil`

while (choice != price_to_find)
  puts "How much (between 1 and 5)?"
  choice = gets.chomp.to_i
end

puts "You won!"