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Ruby Cheat Sheet Cheat Sheet (DRAFT) by

This is a Cheat Sheet for Beginners of Ruby.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

How to print something out on the screen

You can use "­pri­nt". For e.g., print "­Hello World"
You can use "­put­s". For e.g., puts "­Hello World"
When you use print, everything gets printed out on the same line
When you use puts, everything gets printed out on a new line

Variables

Let's say we want to print out the message:
I am 18 years old. I like ice skating. I went ice skating for the first time when I was 18.
You can create variables: 
charac­ter_age = "­18" 
charac­ter­_sport = "ice skatin­g"

To print this message, write:
 	
charac­ter_age = "­18"
charac­ter­_sport = "ice skatin­g"
puts ("I am " + charac­ter_age + " years old.")
puts ("I like " + charac­ter­_sport)
puts ("I went " + charac­ter­_sport + " for the first time when I was " + charac­ter­_age)
 
You can also modify the message half way:

charac­ter_age = "­18"
charac­ter­_sport = "ice skatin­g"
puts ("I am " + charac­ter_age + " years old.")
puts ("I like " + charac­ter­_sport)
charac­ter­_sport = "­cyc­lin­g"
puts ("I went " + charac­ter­_sport + " for the first time when I was " + charac­ter­_age)

It will output:
I am 18 years old. I like ice skating. I went cycling for the first time when I was 18.

Data Types

String­/Text
name = "­Mik­e"

Integer (A full number)
age = 18. Note that you do not need to include quotat­ions.

Floating Point (A number that has a decimal)
number = 18.9

Boolean (on/off, true/f­alse, 1/0)
isfemale = true

Nil (referring to "­not­hin­g". Absence of a value)
flaws = nil

What does .close() do?

def write_data_to_file(file_name)
   a_file.puts('5')
   a_file.puts('Fred')
   a_file.puts('Sam')
   a_file.puts('Jill')
   a_file.puts('Jenny')
   a_file.puts('Zorro')
   a_file.close()
end
The close() is an inbuilt function in Ruby.

Parame­ters: The function does not takes any element.
Return Value: It closes the queue and does not returns anything.

Arrays

friends = Array["Kevin", "Karen", "Oscar"]
puts friends[-2]

It will output: Karen


If you want to select names from index 0 - 2:

friends = Array["Kevin", "Karen", "Oscar"]
puts friends[0, 2]

It will output: Kevin, Karen. Note that is does 
not include Oscar.

Typing input into the terminal

puts "Enter your name: "
name = gets.chomp()
puts "Enter your age: "
age = gets.chomp()
puts ("Hello " + name + ", you are" + age + " years old")
 

What does gets.chomp do?

puts "Enter your name"
name = gets
puts ("Hello " + name + " , you are cool!")

"gets" alone will put ", you are cool!" on a new line.
To mitigate this, we use gets.chomp to ensure that 
"Hello " + name + " , you are cool!" is on one line.

How to print a new line?

print "­Hello\n World"

It will output:
Hello
World

What is Array.new?

 
friends = Array.new

Here we're basically telling Ruby that we want
friends to be an array but we don't want to put
any new values into it just yet

friends[0] = "­Mol­ly"

puts friends[0]

Calcul­ating age when inputting year of birth

require 'date'

def hello()

puts("what year were you born?")
year_born = gets.chomp()
age = Date.today.year - year_born.to_i() - 1 
puts("So you are " + age.to_s + " years old")
end

def
main()
hello()
end

main()

How to print out a quotation mark in a string

puts "­Gir­aff­e\" Academ­y"
It will output: Giraff­e" Academy
 

How to delete extra trailing and whites­pace?

phrase = "   Giraffe Academy  "
puts phrase.st­rip()

It will output "­Giraffe Academ­y"

How to calculate the length of a string?

phrase = "Giraffe Academy"
puts phrase.length()

It will output: 15

How to get a range of text?

phrase = "Giraffe Academy"
puts phrase[0,3]

It will output: Gir

How to find the index position of a string

phrase = "Giraffe Academy"
puts phrase.index("ffe")

It will output the index position it starts at: 4

How to make a string upperc­ase­/lo­wer­case?

phrase = "­Giraffe Academ­y"
puts phrase.up­case() 
puts phrase.do­wnc­ase()

It will output: 
GIRAFFE ACADEMY 
giraffe academy

What is a class?

class Book
   attr_accessor :title, :author, :pages
end

book1 = Book.new()
book1.title = "Harry Potter"
book1.author = "JK Rowling"
book1.pages = 400

puts book1
This class is a template or blueprint for repres­enting a Book inside of the program.
Essent­ially it's like creating your own Data Type.