Ruby Cheat Sheet

A Programming › Ruby cheat sheet in English by ragami

This is a Cheat Sheet for Beginners of Ruby.

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PRs

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

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")

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.

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.

How to print out a quotation mark in a string

puts "Giraffe\" Academy"

It will output: Giraffe" Academy

How to print a new line?

print "Hello\n World"

It will output:
Hello
World

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.

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 make a string uppercase/lowercase?

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

It will output: 
GIRAFFE ACADEMY 
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

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.

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