Introduction to Ruby

This is a very basic introduction to Ruby directed for those without much programming experience. It will cover using the terminal and interative ruby shell (IRB), data types, objects/classes, methods, conditional logic, and running a program from a file in the terminal.

Content source:

Based on the workshop developed by Dessy Deskalov for Ladies Learning Code

Agenda

What is Ruby?

Ruby is a programming language

Why do people love Ruby?

Created in 1993 by Yukihiro Matsumoto, from Japan.

“I hope to see Ruby help every programmer in the world to be productive, and to enjoy programming, and to be happy. That is the primary purpose of the Ruby language.”

Ruby in the Command Line

The IRB (“Interactive Ruby Shell”) is an interactive command-line interpreter that can be used to test code quickly.

OS X

Applications -> Utilities -> Terminal

Windows

(C:\windows\system32\cmd.exe)

Start -> All Programs -> Accessories -> Command Prompt

Using IRB (Interactive Ruby)

Type IRB into the console

irb

Then you’ll see somthing like this:

ruby-1.9.2-p290 :001 >

What can Ruby do?

Try typing:

irb(main):001:0>puts "Hello World"
    Hello World
    => nil

puts is the basic command to print something out in Ruby. => nill is the result of the expression.

Math:

> 1 + 1
=> 2

> 462 * 86
=> 39732

Data Types

Data Types

Numbers without decimals are called INTEGERS. We just did some math with some integers.

Letters, words, and sentences are called STRINGS. We tell Ruby that we are intending to use a string by wrapping it in quotes.

Some other data types in Ruby:

Variables

How do Variables Work?

What if we want to remember the result of some of this math? Assign the result to a variable.

irb(main):007:0> a = 3 ** 2 
=> 9 
irb(main):007:0> b = 4 ** 2
=> 16
irb(main):007:0> Math.sqrt(a+b)
=> 5.0

We can also assign a String to a variable

irb(main):007:0> my_name = "John Doe" 
 => "John Doe"

Telling Ruby the variable my_name points to the string “John Doe”.

Objects

Objects, Objects, Everywhere!

Everything in Ruby is an Object.

Great, but what is an object?

An OBJECT is an INSTANCE of a CLASS.

A what is a what of a what?

Classes

Before she can do something with an object, Ruby needs to know what kind of object she’s dealing with.

irb(main):007:0> 1+1 
=> 2 
irb(main):007:0> "1" + "1" 
=> "11"

So how do classes help?

Classes define objects and what can be done with them.

The Integer class will have different instructions for “+” than the String class.

Objects have an IS A relationship with their classes.

Methods

The actions you can perform on an object are called methods.

Every object that IS A class can perform the methods defined by that class.

irb(main):010:0> def hi 
irb(main):011:1>   puts "Hello World!" 
irb(main):012:1> end 
=> :hi

Integer Methods

The Integer class has instructions for the methods next, odd?, and even?.

You can call next, odd?, and even? on ALL Objects that are Integers

String Methods

The String class has instructions for the methods capitalize, upcase, and reverse.

You can call capitalize, upcase, and reverse on ALL Objects that are Strings.

Playing with Integers

> 99.zero?
=> false

> 99.odd?
=> true

> 99.even?
=> false

Another example

> title = "Peter Rabbit"
> title.reverse
   
What am I supposed to do with this object? reverse
Do I know how to do that action on this object? Yes! The String class defines a method reverse and returns the string in reverse order. 
=>"tibbaR reteP"

Fun with strings

> "universityoftoronto".capitalize
=> "Universityoftoronto"

> "universityoftoronto".upcase
=> "UNIVERSITYOFTORONTO"

> "UNIVERSITYOFTORONTO".downcase
=> "universityoftoronto"

> "universityoftoronto".reverse
=> "otnorotfoytisrevinu"

Method Errors

> myNumber = 123
> myNumber.reverse
   
What am I supposed to do with this object? reverse
Do I know how to do that action on this object? No. The Integer class does not define a method reverse. 
=> NoMethodError: undefined method `reverse' for 123:Fixnum
    from (irb):1
    from :0

Methods and Objects and Classes, Oh My!

How can I find the class of my object?

> mysteryObject = "What am I?"
> mysteryObject.class
=> String

How do I know what methods I can call on my object?

> mysteryObject.methods
=> ["upcase!", "zip", "pretty_print_cycle"....]

How do I know what those methods do?

Look them up here

Built-in Classes

Ruby comes with many built-in classes that we can use.

String, Integer, File, Hash, Array…

You can read about all the built-in objects here

Custom Classes

What if we want to define our own class?

Let’s return to the method hi we wrote (and improve it)

irb(main):010:0> def hi(name) 
irb(main):011:1>   puts "Hello #{name}!" 
irb(main):012:1> end 
=> :hi

The method hi takes the name as a parameter.

#{name} is Ruby’s way of inserting something into a string

irb(main):024:0> class Greeter
irb(main):025:1>   def initialize(name)
irb(main):026:2>     @name = name
irb(main):027:2>   end

irb(main):028:1>   def say_hi
irb(main):029:2>     puts "Hi #{@name}!"
irb(main):030:2>   end
irb(main):034:1> end
=> nil

The new keyword here is class. This defines a new class called Greeter and a bunch of methods for that class. Also notice @name. This is an instance variable, and is available to all the methods of the class. As you can see it’s used by say_hi.

Custom Classes

Lets create a Greeter object and use it:

irb(main):035:0> greeter = Greeter.new("Pat")
=> #
irb(main):036:0> greeter.say_hi
Hi Pat!
=> nil

The method new is a unique type of method, which is predefined in the Ruby library. The new method belongs to the class methods. The initialize method is a special type of method, which will be executed when the new method of the class is called with parameters.

Custom Classes: Exercise

Let’s make a class Calculator that has the methods add and subtract

irb(main):035:0> my_calculator = Calculator.new
=> # 
irb(main):036:0> my_calculator.add(5,2)
7
=> nil
irb(main):036:0> my_calculator.subtract(5,2)
3
=> nil

Custom Classes: Solution

irb(main):024:0> class Calculator

irb(main):025:1>   def add(x,y)
irb(main):026:2>     puts x + y
irb(main):027:2>   end

irb(main):028:1>   def subtract(x,y)
irb(main):029:2>     puts x - y
irb(main):030:2>   end
irb(main):034:1> end
=> nil

Writing a Program

Open any text editor, add the same code, and save it as twitter.rb. Remember the directory you have saved it in.

tweet = "I'm writing my first program and it's pretty rad."
puts tweet.length

To run your program, type quit to exit from IRB, and then type:

ruby twitter.rb

Getting Input From the User

The real Twitter…

Asks you to type something.

Tells you how many characters you’re working with.

So far, we’ve just been putting our tweet directly into the program.

Asking for Input

The puts method is used for output, and the gets method is used for input. Try this:

The gets method warns Ruby that you’re about to speak.

> tweet = gets
 all-string
I'm learning Ruby with #ladieslearningcode

=> "I'm learning Ruby with #ladieslearningcode\n"

Wait, we didn’t type \n in our tweet. What is that?

Asking for Input

The \n is there because you hit the enter button after you typed your tweet. It represents a new line, and counts as exactly one character. To get rid of it, do this:

> tweet = gets.chomp
 all-string
I'm learning Ruby with #ladieslearningcode

=> "I'm learning Ruby with #ladieslearningcode"

Asking for Input

Now try this:

> tweet = gets.chomp
 all-string
I'm a lady learning code with @learningcode #ladieslearningcode

=> "I'm a lady learning code with @learningcode #ladieslearningcode"

> puts tweet
 all-string
I'm a lady learning code with @learningcode #ladieslearningcode
=> nil

Back to your Twitter Program

Working with your group, modify your Twitter program to do the following:

  1. Ask (politely!) for a tweet from the user.

  2. Store the tweet in a variable, without \n

  3. Output the tweet the user gave.

  4. Output the number of characters in the tweet.

  5. Output how many more characters the user can add until they hit 140 characters.

(answers in assignments/twitter_3.rb)

Giving Output Based on Input

Twitter…

Lets you send your tweet if it is 140 characters or less

Tells you that your tweet is too long to send otherwise.

Giving Output Based on Input

So far we know how to determine the length of the user’s tweet.

We don’t know how to tell them whether they can or cannot send their tweet, depending on it’s length.

Conditional Logic

Programming is writing out sets of simple instructions for the computer to follow.

Let’s break down out tweet logic into simple instructions.

Conditional Logic

We want our program to …

if the tweet is greater than 140 characters, tell the user that they cannot send their tweet

if the tweet is less than or equal to 140 characters, tell the user that they can send their tweet

Conditional Logic

Logical operators

> 200 > 140

=> true

> 200 < 140

=> false

Conditional Logic: IF Statements

Try the code below in IRB:

>if 200 > 140 
>  puts true
>end

=> true

Conditional Logic: IF/ELSE Statements

Try the code below in IRB:

>if 200 > 140 
> puts true
>else
  puts false
>end

=> true

Conditional Logic in Our Simple Twitter

tweet = gets.chomp

if tweet.length <= 140
  puts "Tweet your heart out!"
end

Conditional Logic in Our Simple Twitter

tweet = gets.chomp

if tweet.length <= 140
  puts "Tweet your heart out!"
else
  puts "Your tweet is too long!"
end

While Loops

What if you want to be able to tell your program when to stop running? Create a new program with the following code.

puts "Hi!"
greeting = gets.chomp

while greeting != "bye!"
  puts greeting
  greeting = gets.chomp
end

This is called a while loop. The program will run while the user inputs anything other than “bye!”

Arrays

[1, 2, 3, 4, 5]

[7, 13, 14, 16, 14, 48]

["ladies", "learning", "code"]

Iterating through an Array

 > my_numbers = [1, 2, 3, 4, 5]
 > my_numbers.each do |i| 
 >  puts i**2 
 > end

Final Task

Credits

Inspired by Chris Pine’s Learn to Program

Resources

Learn Ruby in 20 Minutes

why’s poignent guide to Ruby

Ruby Koans

Rails

Lots more!

And finally…

Thank you!

Creative Commons License by Ladies Learning Code