Ruby Code Guide

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!"

Mathematics

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

Methods

def hi
    puts "Hello World!"
end

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

Classes

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.

LOOPING

@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
"

Whitespace

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

example = "New line \nhere"