Ruby Basics Help Sheet

RUBY-1: Comments

This is an example comment

RUBY-2: Variables

variable = some_value name = "Tobi" name # => "Tobi" sum = 18 + 5 sum # => 23

RUBY-3: Console puts

puts something puts "Hello World" puts [1, 5, "mooo"]

RUBY-4: Call a method

object.method(args) string.length array.delete_at(2) string.gsub("ae", "ä")

RUBY-5: Define a method

def name(parameter) #method body end def greet(name) puts "Hi there " + name end

RUBY-6: Equality

object == other true == true # => true 3 == 4 # => false "Hello" == "Hello" # => true

RUBY-7: Inequality

object != other true != true # => false 3 != 4 # => true

RUBY-8: Decisions with if

if condition # happens when true else # happens when false end if input == password grant_access else deny_access end

RUBY-9: Constants

CONSTANT = some_value PI = 3.1415926535

RUBY-10: Strings

'This is a string' 'This is a string with an #{expression}' example = 'This is another string' example.length

RUBY-11: Concatentation

string + string2 "Hello " + "reader"

RUBY-12: Substitute

string.gsub(a_string, substitute) "Bill".gsub("ill", "oo") # => "Boo"

RUBY-13: String Access

string[position] "Hello"[1] # => "e"

RUBY-14: Arrays

[contents] [] # empty array ["Rails", "fun", 5] array.size [].size # => 0 [1,2,3].size # => 3 ["foo", "bar"].size # => 2 array[position]

RUBY-15: add an array element

array << element array = [1,2,3] array << 4 array # => [1,2,3,4] array[4] = 5 array.delete_at(i) array.each do |e| .. end persons.each do |p| puts p.name end numbers.each do |n| n = n * 2 end

RUBY-16: Hashes

Hashes associate a key to some value. You may then retrieve the value based upon its key. This construct is called a dictionary in other languages, which is appropriate because you use the key to "look up" a value, as you would look up a definition for a word in a dictionary. Each key must be unique for a given hash but values can be repeated.

Hashes can map from anything to anything! You can map from Strings to Numbers, Strings to Strings, Numbers to Booleans... and you can mix all of those! Although it is common that at least all the keys are of the same class. Symbols are especially common as keys. Symbols look like this: :symbol. A symbol is a colon followed by some characters. You can think of them as special strings that stand for (symbolize) something! We often use symbols because Ruby runs faster when we use symbols instead of strings.

{key => value} {:hobby => 'programming'} {42 => 'answer', 'score' => 100, :name => 'Tobi'} hash[key] hash = {:key => 'value'} hash[:key] # => 'value' hash[foo] # => nil hash[key] = value hash = {:a => "b"} hash[:key] = "value" hash # => {:a=>b, :key=>"value"} hash.delete(key) hash = {:a => 'b', :b => 10} hash.delete(:a) hash # => {:b=>10}

THRUBY-1: TH Ruby Basics

Interactive environment: irb (in the terminal)

puts "hello world!"


3**2 // this means three to the square of two Math.sqrt(a+b) // this is a static method


def hi puts "Hello World!" end

  • if the method does not take parameters, then you do not need to define the curly braces


class Greeter attr_accessor :name def initialize(name = "World") @name = name end def say_hi puts "Hi #{@name}!" end def say_bye puts "Bye #{@name}, come back" end end greeter = Greeter.new("Pat")

  • Using attr_accessor defined two new methods for us, name to get the value, and name= to set it.


@names.each do |name| puts "Hello #{name}!" end # Say bye to everybody def say_bye if @names.nil? puts "..." elsif @names.respond_to?("join") # Join the list elements with commas puts "Goodbye #{@names.join(", ")}. Come back soon!" else puts "Goodbye #{@names}. Come back soon!" end end

Input and Output

Giving input to the variable.

  • puts auto creates \n
  • print does not

# name = "Jason" print "Please enter your name: " name = gets # this is what is going to take the input puts "Hello #{name}!"

THRUBY-2: Ruby Strings

What are Strings?

  • Using double quotes when creating a string will cause variables in the string to be interpolated.

# this will all print out as is name="Dennis" string = <<-STRING Hello My name is #{name} Workspaces is fun! STRING thisAlsoWorks="This is a multiline String "


\n -> new line \s -> space \t -> new tab

example = "New line \nhere"

THRUBY-2: Ruby Numbers

THRUBY-2: Ruby Methods