Welcome to
Ladies Learning Code

In partnership with

Learning to Program
with Ruby

Content created by Dessy Deskalov

Agenda

• What is Ruby?
• The Anatomy of a Programming Language
• Strings, Numbers and Varaibles
• Objects and Methods
• Control Flow
• Exercises, Puzzles and Challenges

Introductions!

• Nathan Feaver
• Senior Developer - AgileStyle

The Slides

http://goo.gl/NuGuG5

What is Ruby?

There are two things you should know about your computer.

1. Your computer speaks a different language.

This is how your computer wishes you could speak to it:

This is where a programming language comes in.

A programming language is a language that is relatively easy for you to learn, but can also be understood by the computer.

It's the middle ground between English and the language that the computer understands.

2. Your computer is not very smart.

Your computer can only do what you tell it to if you give it exact instructions.

People vs. Computers

Suppose you had to teach a person how to make a peanut butter sandwich. You might give the person an easy to follow recipe.

People vs. Computers

1. Toast two slices of bread

2. Spread peanut butter on one slice of bread

3. Spread jam on the other slice of bread

4. Put the two pieces of bread together

5. Put the sandwich on a plate and serve it

People understand GENERAL instructions.

We left out some parts of the process, but a person could figure out:

Where to find the ingredients

To use a butter knife to spread the peanut butter

To put the bread in a toaster in order to toast it

etc, etc, etc (there are many little steps)

Computers understand EXACT instructions.

This same recipe for a computer would be much, much longer.

1. Toast two slices of bread

What is bread?

Where is it found?

How do I open the bag?

What is a slice?

How do I slice the bread?

How do I "toast"?

What is a toaster?

How do I use a toaster?

etc, etc, etc

2. Spread peanut butter on one slice of bread

What is peanut butter?

How do I "spread" peanut butter?

What is a butter knife?

Where is it found?

How do I open the knife drawer?

Which slice do I spread it on?

How much peanut butter do I spread?

etc, etc, etc

Back to programming languages.

A programming language makes it easier for you to give the computer instructions.

It's made up of simple elements, that when combined together, are used to write a set of instructions that the computer then breaks down and interprets as its own language.

You've just learned what programming is!

Programming is writing out exact instructions that your computer can follow to do things.

Why Ruby Rocks!

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 is fun, it's easy to learn, and the syntax is very forgiving.

This is some code in Java:

class Person {
  private String name, int age;

  public void setName(String name) {
    this.name = name;
  }

  public String getName() {
    return name;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public String getAge() {
    return age;
  }
}

The equivalent code in Ruby looks like this:

class Person
  attr_accessor :name, :age
end
          

Meet Ruby

Ruby is an interpreter.

Ruby understands the Ruby language and translates it into computer language.

We can give Ruby instructions with files or with IRB (Interactive Ruby).

Time to see Ruby in action!

IRB is like text messaging with Ruby.

You'll ask Ruby to do something, and she will respond.

Applications -> Utilities -> Terminal

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

Ruby can do math, and she can do it much quicker than a person can.

> 1 + 1
=> 2

> 462 * 86
=> 39732

Variables

> llc = "ladieslearningcode"
=> "ladieslearningcode"

Variables in Ruby Language

You told Ruby the variable llc points to the string "ladieslearningcode".

Ruby files "ladieslearningcode" away under llc.

Next time you want the string "ladieslearningcode", you just tell Ruby to use the value of llc.

Variables Can (And Often Do!) Vary

A variable is called just that because the object it points to can change.

> llc = "a lady learning code"
=> "a lady learning code"

llc "a lady learning code"

Now let's ask for the value of llc.

> llc
=> "a lady learning code"

Let's try some more

> llc = 99
=> 99

llc 99

Let's ask for the value of llc once again.

> llc
=> 99

The More the Merrier

Let's introduce another variable.

> copy_cat = llc
=> 99

llc 99 copy_cat

Let's ask for the value of each variable.

> llc
=> 99

> copy_cat
=> 99

> llc = "ladieslearningcode"
=> "ladieslearningcode"

Integers and Strings

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.

Objects, Objects, Everywhere!

Classes

Classes so far

Let's try some more!

Hint: Remember, an Object IS A instance of a Class!

Classes and Ruby

Ruby uses what she knows about an object to perform actions on it.

When you give Ruby a set of instructions, she asks the following:

• What am I supposed to do with this object?
• Do I know how to do that action on it?

If she knows how to perform the action on the object, she does it. If she doesn't, you'll get an error.

Methods

Integer Methods

String Methods

Classes and Ruby

Let's walk through some examples from Ruby's perspective

>counter = 0
>counter.next

=>1

Playing with Integers

> 99.zero?
=> false

> 99.odd?
=> true

> 99.even?
=> false

Another example

>title = "Peter Rabbit"
>title.reverse

=>"tibbaR reteP"

Fun with strings

> "ladieslearningcode".capitalize
=> "Ladieslearningcode"

> "ladieslearningcode".upcase
=> "LADIESLEARNINGCODE"

> "LADIESLEARNINGCODE".downcase
=> "ladieslearningcode"

> "ladieslearningcode".reverse
=> "edocgninraelseidal"

Method Errors

>myNumber = 123
>myNumber.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?

Built-in Classes

Custom Classes

What about City and Playing Card and Duck?

We won't do it today, but you can make your own classes and objects! Here's a teaser for you to start exploring on your own

class Duck
  attr_accessor :name
  def quack
    puts "Quack, quack!"
  end
end

> donald = Duck.new
  donald.name = "Donald Fauntleroy Duck"
  donald.quack
=> "Quack, quack!"

Variables and methods

> llc = "ladieslearningcode"

> llc.reverse
=> "edocgninraelseidal"

> llc
=> "ladieslearningcode"

Wait. Why didn't it change?

llc is still pointing to "ladieslearningcode". You didn't tell it to point to a different string.

llc "ladieslearningcode"

If you want the value to change, you have to set it to something else.

Let's Try One More

> llc.length

=> 18

Doing like Twitter does.

> tweet = "I'm writing my first program at the @learningcode
Intro to Ruby workshop!"

=> "I'm writing my first program at the @learningcode 
Intro to Ruby workshop!"

> tweet.length

=> 73

Writing Our First Program

Open any text editor, add the same code, and save it as twitter.rb in your llc directory.

tweet = "I'm writing my first program at the @learningcode
Intro to Ruby workshop!"
tweet.length

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

ruby twitter.rb

Outputting Text to the Screen

IRB is like back-and-forth text messaging.

A program has to be told when to output something

Modify your program:

tweet = "I'm writing my first program at the @learningcode
Intro to Ruby workshop!"
puts tweet.length

Recap Slide

Puzzle One - Variables

Open puzzle_1.rb in the puzzles folder, and write down the output you expect to see if you were to run this script.

If you're not sure of something, remember that you can type irb again and try it out.

Getting Input From the User

The real Twitter...

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

I'm learning Ruby with #ladieslearningcode

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

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

I'm learning Ruby with #ladieslearningcode

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

Asking for Input

Now try this:

> tweet = gets.chomp

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

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

> puts tweet

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

What's nil? It's nothing, don't worry.

You asked Ruby to output your tweet, and Ruby did just that.

Remember that in IRB, Ruby always responds to your message. This time, it gave the output, and had nothing else to say, so it returned nil.

nil is also an Object, and it just represents nothing.

Back to your Twitter Program

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

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: Greater Than

The math symbol for greater than is >

Try the code below in IRB:

> 200 > 140

=> true

Conditional Logic: Greater Than

Now try:

> number_of_characters = 200

=> 200

> number_of_characters > 140

=> true

Conditional Logic: Greater Than

Now try:

> number_of_characters = 80

=> 80

> number_of_characters > 140

=> false

Conditional Logic: Less Than

The math symbol for less than is <

Try the code below in irb

> llc = "ladieslearningcode"

=> "ladieslearningcode"

> llc.length < 140

=> true

Conditional Logic in Our Simple Twitter

Let's simplify our if statements.

Remember that we're storing the user's tweet in the variable tweet.

Conditional Logic in Our Simple Twitter

Original if statements:

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

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

Try it out!

Replace the puts statements in your Twitter program with the code below. (see assignments/twitter_4.rb if needed)

if tweet.length > 140
  puts "Your tweet is too long!"
end

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

Using the tweets from tweets.txt, try out your new script! What's the problem here? What do you notice happened when using the tweets in tweets.txt?

Your First Bug!

We're not actually taking into account all possible tweet lengths.

Programming problems can be solved many different ways.

We'll look at three different solutions.

First (Worst) Solution

Since we're only missing one case, the case where the tweet is exactly 140 characters, we can just add another if statement.

First (Worst) Solution

Add this last if statement to the bottom of your file: (see assignments/twitter_5.rb if needed)

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

The == operator checks that the value of the objects on either side of it are equal.

Refactoring Our Code

Programmers are always refactoring (re-structuring, re-organizing) their code to make it cleaner and more readable. Right now is a great time to do that.

Refactoring Our Code

Three if statements are unnecessary. We can actually combine all of these if statements into one, like so:

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

(see assignments/twitter_6.rb if needed)

if .. elsif

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

In the above code, if the first statement doesn't evaluate to true, then the next one is attempted, and so on.

if .. elsif

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

Only one puts statement is ever executed. The statements are evaluated in the order they are written, so the first one to evaluate to true is the only one executed.

if .. elsif

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

If none of the statements evaluate to true, then none of the puts statements are executed.

Second Solution

Notice that the line puts "Tweet your hear out!" is unnecessarily repeated?

Let's cut it out by replacing the entire if statement with the code below:

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

(see assignments/twitter_7.rb if needed)

Less than or equal to with <=, Greater than or equal to with >=

The <= operator checks for equality as well.

Checking for equality with greater than works exactly the same way, using the >= operator.

Third Time's a Charm

This is better, but look at the logic closely. Do we really even need to specify the second condition?

Replace your code again with the code below:

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

(see assignments/twitter_8.rb if needed)

if .. else

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

Just like with if .. elsif, only one puts statement is ever executed. The difference here is that one of the puts statements is always executed.

if .. else

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

The else is there are a catch-all. You can think of it like a last resort. If none of the other options are true, then just execute the puts statement after the else.

Hello, Operator?

Recap Slide

Puzzle Two - Conditionals

Look at the program in puzzle_2.rb.

The program asks the user for the month of their birthday, and then outputs a message about the season the user celebrates their birthday in.

Puzzle Two - Conditionals

Which months does this program consider to be spring, summer, winter, and fall?

Simplify the logic to make the program as few lines of code as possible?

Goal: 20 lines!

Loopy

What if you want to be able to tell your program when to stop running? Create a new program with the following code, or run the program in assignments/loop_1.rb:

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!"

What if we know exactly how many times the program needs to do that same thing?

Again, there are several ways to do this.

Tell me exactly how many times

Create a new program with the following code, or use run the program in assignments/loop_2.rb:

3.times do
  puts "Hip-Hop-Hooray!"
  sleep 1
end

This program will output "Hip-Hip-Hooray!" exactly 3 times.

Tell me exactly how many times

3.times do
  puts "Hip-Hop-Hooray!"
  sleep 1
end

The sleep 1 tells the program to wait 1 second after outputting each statement.

Try taking it out to see what happens. Not as exciting.

Count from 1 to 5

Create a new program with the following code, or use run the program in assignments/loop_3.rb:

puts "Okay, on the count of 5 ..."
[1, 2, 3, 4, 5].each do |i|
  puts i
  sleep 1
end
puts "GO!"

Count from 1 to 5

puts "Okay, on the count of 5 ..."
[1, 2, 3, 4, 5].each do |i|
  puts i
  sleep 1
end
puts "GO!"

This program loops through each Integer from 1 to 5, and outputs the Integer, again sleeping for 1 second in between.

Counting down

Maybe we want a program that simulates a countdown.

Create a new program with the following code, or use run the program in assignments/loop_4.rb:

99.downto(1).each do |i|
  puts "#{i} bottles of beer on the wall, #{i} bottles of beer.
        Take one down, pass it around,
        and now there are #{i - 1} bottles of beer on the wall!"
  sleep 0.5
end

Counting down

99.downto(1).each do |i|
  puts "#{i} bottles of beer on the wall, #{i} bottles of beer.
        Take one down, pass it around,
        and now there are #{i - 1} bottles of beer on the wall!"
  sleep 0.5
end

This program moves through each Integer from 99 down to 1, and outputs the Integer, this time sleeping for half a second in between.

Counting down

Wait a second, how did we get an Integer in that String?

puts "#{i} bottles of beer on the wall, #{i} bottles of beer.
      Take one down, pass it around,
      and now there are #{i - 1} bottles of beer on the wall!"
          

You can use the syntax #{my_variable} inside of the String, and Ruby will treat the variable exactly like a String.

String Interpolation

> lesson = "Ruby"

=> "Ruby"

> tweet = "I am learning all about #{lesson} at the 
#ladieslearningcode workshop"

=> "I am learning all about Ruby at the 
#ladieslearningcode workshop"

String Interpolation

> lesson = "String Interpolation"

=> "String Interpolation"

> tweet = "I am learning all about #{lesson} at the 
#ladieslearningcode workshop"

=> "I am learning all about String Interpolation at the 
#ladieslearningcode workshop"

What if we don't want to count, but we have a set of something else we want to loop over?

Create a new program with the following code, or use run the program in assignments/loop_5.rb:

puts "And the lucky numbers are ..."
[7, 13, 14, 16, 14, 48].each do |i|
  puts i
  sleep 1
end
puts "With a bonus number 32!"

Leaving early

What if we want to be able to leave a loop early, before we have finished looping?

We need a way to tell Ruby to stop looping. We do that using the command break.

break tells the loop to stop where it is.

Leaving early

Create a new program with the following code, or run the program in assignments/loop_6.rb:

puts "Time to play Blackjack! Let's simulate a losing game."

sum = 0
[2, 4, 10, 9, 3].each do |card|
  sleep 1
  puts "Dealing a card with value #{card}"
  sum = sum + card

  if sum > 21
    puts "You lost!"
    break
  else
    puts "Hit me!"
  end
end

Loops + Arrays = <3

Every time you were looping, regardless or whether you were counting using [1, 2, 3, 4, 5], or just looping over [7, 13, 14, 16, 14, 48], you were using arrays.

An array is simply a collection of objects. Loops are used to move from one element of an array to another.

Array

There are many methods on Array, as well.

Back in IRB, let's create an array of winning lottery numbers and store it in the variable lottery.

> lottery = [7, 13, 14, 16, 14, 48]

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

Methods that do NOT modify the array

> lottery.join(', ')

=> "7, 13, 14, 16, 14, 48"

> lottery

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

Methods that do NOT modify the array

> lottery[0]

=> 7

> lottery[1]

=> 13

> lottery[6]

=> nil

Methods that do NOT modify the array

> lottery.uniq

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

> lottery

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

Methods that DO modify the array

> lottery.delete_at(0)

=> 7

> lottery

=> [13, 14, 16, 14, 48]

Methods that DO modify the array

> lottery << 92

=> [13, 14, 16, 14, 48, 92]

> lottery

=> [13, 14, 16, 14, 48, 92]

Puzzle 3 - Arrays

What will be the output of puzzle 3?

Remember to think about which methods modify the array, and which do not.

Ruby on Rails

Ruby became popular mostly because of Rails.

Ruby on Rails

Imagine you're building a house.

Ruby on Rails

Many people before you have built houses.

Why do the boring work?

Rails gives you the foundation, the plumbing, the electrical work, and the structural walls.

Ruby on Rails

Rails was extracted from work done on Basecamp at 37signals. (2004)

A Program All Your Own

Let's write a program from scratch.

For the biggest challenge:

Create a new document called colours.rb and write the program from scratch.

For a little bit of guidance:

Open the file colours.rb in the assignments folder.

Answers can be found in assignments/answers/colours.rb

Favourite Colour

Write a program that does the following:

An (Addictive) Program All Your Own

Let's write something more complicated from scratch.

For the biggest challenge:

Create a new document called blackjack.rb and write the program from scratch.

For a little bit of guidance:

Open the file blackjack.rb in the assignments folder.

Answers can be found in assignments/answers/blackjack.rb

Blackjack Game

We're going to create a Blackjack game with some simplified rules.

Blackjack Game

Blackjack Game

If the player manages to make it through the hitting cycle without winning or losing, the dealer receives cards until their sum is greater than or equal to 17.

The sum of the player's cards and the sum of the dealer's cards are compared.

If the dealer's sum is greater than 21, then the player wins.

Otherwise if the player's sum is greater than the dealer's sum, then the player wins.

Otherwise if the player's sum is equal to the dealer's sum, then there is a tie.

In all other cases, the player loses.

Credits

Inspired by Chris Pine's Learn to Program

Resources

Learn Ruby in 20 Minutes

why's poignant guide to Ruby

RubyLearning.org - Core Ruby Course

Rails

Lots more!

And finally...

Thank you!

Big, big thank you to
Startup Edmonton for hosting us in their space!