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<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Intro to Ruby ~ Girl Develop It</title>
<meta name="description" content="This is the official Girl Develop It Core Intro to Ruby course. The course is meant to be taught in five two-hour sessions. Each of the slides and practice files are customizable according to the needs of a given class or audience.">
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</head>
<body>
<div class="reveal">
<!-- Any section element inside of this container is displayed as a slide -->
<div class="slides">
<!-- Opening slide -->
<section>
<img src = "img/gdi_logo_badge.png">
<h3>Intro to Ruby</h3>
<h4>Class 2</h4>
</section>
<section>
<h3>Welcome!</h3>
<div class = "left-align">
<p>Girl Develop It is here to provide affordable and accessible programs to learn software through mentorship and hands-on instruction.</p>
<p class ="green">Some "rules"</p>
<ul>
<li>We are here for you!</li>
<li>Every question is important</li>
<li>Help each other</li>
<li>Have fun</li>
</ul>
</div>
</section>
<!-- Homework Review - 10 min -->
<section>
<h3>Homework Discussion</h3>
<p>How was last week's homework? Do you have any questions or concepts that you'd like to discuss?</p>
</section>
<!-- Block 1 30 minutes -->
<section>
<h3>Review</h3>
<ul>
<li>Arithmetic and variables</li>
<li>Data types</li>
<li>Text editor, command line, and ruby shell</li>
</ul>
</section>
<section>
<h3>What we will cover today</h3>
<ul>
<li class ="fragment">Boolean Expressions and Conditionals</li>
<li class ="fragment">Loops</li>
<li class ="fragment">Collections</li>
</ul>
</section>
<section>
<h3>Booleans</h3>
<p>A <strong>boolean</strong> is a basic data type. It can have only two values: true or false.</p>
</section>
<section>
<h3>Boolean Expressions</h3>
<p>Code that compares values and returns True or False is called a <strong>Boolean expression</strong></p>
<ul>
<li>Test for equality by using `==`. We can't use `=` because that is used for assignment</li>
<li>Test for greater than and less than using `>` and `<`</li>
</ul>
</section>
<section>
<h3>Boolean Expressions cheat sheet</h3>
<table>
<tr>
<td>a == b</td>
<td>a is equal to b</td>
</tr>
<tr>
<td>a != b</td>
<td>a does not equal b</td>
</tr>
<tr>
<td>a < b</td>
<td>a is less than b</td>
</tr>
<tr>
<td>a > b</td>
<td>a is greater than b</td>
</tr>
<tr>
<td>a <= b</td>
<td>a is less than or equal to b</td>
</tr>
<tr>
<td>a >= b</td>
<td>a is greater than or equal to b</td>
</tr>
</table>
<p>Learn more about logical operators in Ruby <a href="http://www.tutorialspoint.com/ruby/ruby_operators.htm" alt="Operators tutorial">here</a>.</p>
</section>
<section>
<h3>Boolean Expressions practice</h3>
<pre><code class="ruby">
a = 3
b = 4
puts a != b
puts a <= 3
puts a >= 4
a = 5
b = 5
puts a == b
c = a == b # Combine comparison and assignment
puts c
puts 3 < 5
</code></pre>
<p>Remember: Equals does not equal "equals equals"</p>
<p> <a href="http://ruby.learncodethehardway.org/book/ex27.html">Further reading </a> on boolean expressions...</p>
</section>
<section>
<h3>Boolean Expressions</h3>
<p>A boolean expression evaluates to true or false. It can also have multiple parts, joined by AND (&&) or OR (||).</p>
<table>
<tr>
<th>EXPRESSION</th>
<th>EVALUATES TO</th>
</tr>
<tr>
<td>true && true</td>
<td>true</td>
</tr>
<tr>
<td>true && false</td>
<td>false</td>
</tr>
<tr>
<td>false && false</td>
<td>false</td>
</tr>
<tr>
<td>true || true</td>
<td>true</td>
</tr>
<tr>
<td>true || false</td>
<td>true</td>
</tr>
<tr>
<td>false || false</td>
<td>false</td>
</tr>
<tr>
<td>not (true && false)</td>
<td>true</td>
</tr>
</table>
<p> <a href="http://ruby.learncodethehardway.org/book/ex28.html">Further practice </a> on boolean expressions...</p>
</section>
<section>
<h3>Let's Develop It</h3>
<p>Take a few minutes and experiment with boolean expressions in IRB. You can start with the examples below.</p>
<pre><code class="ruby">
true && false
1 == 1 && 2 > 37
"boop" == "bip" || 7 == 8
false || true
89 > 88 || 89 < 90
true || not(1 == 1 || 2 == 65)
</code></pre>
</section>
<section>
<h3>Putting Booleans to Work</h3>
<p>So, what's the value of knowing if a statement is true or false? Often, you'll use that to control whether a piece of code will execute or not.</p>
<pre><code class="ruby">
user_guess = gets.chomp.to_i
secret_number = 312
if user_guess < secret_number
puts "Too low!"
elsif user_guess > secret_number
puts "Too high!"
else
puts "You guessed it. Wow maybe you're psychic...."
end
</code></pre>
<p>Can you tell what this code does?</p>
</section>
<section>
<h3>Conditionals</h3>
<p>When we want different code to execute depending on certain criteria, we use a <strong>conditional</strong></p>
<p>We achieve this using <strong>if</strong> statements and boolean expressions.</p>
<pre><code class="fragment ruby">
if x == 5
puts 'x is equal to 5'
end
</code></pre>
</section>
<section>
<h3>Conditionals</h3>
<p>We often want a different block to execute if the statement is false. This can be accomplished using <strong>else</strong>.</p>
<pre><code class="fragment ruby">
if x == 5
puts 'x is equal to 5'
else
puts 'x is not equal to 5'
end
</code></pre>
</section>
<section>
<h3>Conditionals</h3>
<p>The following shows some examples of conditionals with more complex boolean expressions:</p>
<pre><code class="ruby">
# And
if x > 3 && y > 3
puts 'Both values are greater than 3'
end
# Or
if x != 0 || y != 0
puts 'The point x,y is not on the x or y axis'
end
# Not
if not(x > y)
puts 'x is less than y'
end
</code></pre>
</section>
<section>
<h3>Chained conditionals</h3>
<p>Conditionals can also be <strong>chained</strong>.</p>
<p>Chained conditionals use <strong>elsif</strong> to test if additional statements are true. The single 'else' action will only happen if all preceding conditions are false.</p>
<p>For example:</p>
<pre><code class="fragment ruby">
if x > 10
puts "x is greater than 10"
elsif x <= 10 && x > 0
puts "x is a number between 1 and 10"
else
puts "Wow, don't be so negative, dude"
end
</code></pre>
</section>
<!-- Let's develop it: 10 minutes -->
<section>
<h3>Let's Develop It</h3>
<p>Write a program in your text editor that uses conditionals and user input to allow the user to play an adventure game.</p>
<p>"gets.chomp" is the value of user input at the command line, with the trailing whitespace chomped off. To do math with it, convert it to an integer with the ".to_i" method</p>
<pre><code>
input = gets.chomp.to_i
</code></pre>
<p>Run your program by calling it with Ruby from the command line.</p>
<pre><code>
$ ruby program_name.rb
</code></pre>
</section>
<section>
<h3>Let's Develop It Example</h3>
<pre><code class="ruby">
# adventure.rb
puts "A vicious dragon is chasing you!"
puts "Options:"
puts "1 - Hide in a cave"
puts "2 - Climb a tree"
input = gets.chomp
if input == '1'
puts "You hide in a cave. The dragon finds you and asks if you'd like to play Scrabble. Maybe it's not so vicious after all!"
elsif input == '2'
puts "You climb a tree. The dragon can't find you."
else
puts "That's not a valid option."
end
</code></pre>
<pre><code class="ruby">
#command line
ruby dragon.rb
</code></pre>
</section>
<!-- Block 2 25 minutes -->
<section>
<h3>Loops</h3>
<p>It is often useful to perform a task and to repeat the process until a certain point is reached.</p>
<p>The repeated execution of a set of statements is called <strong>iteration</strong>, or, more commonly, a loop.</p>
<p>One way to achieve this, is with the <strong>while</strong> loop.</p>
<pre><code class="ruby">
x = 10
while x > 0
puts "Loop number #{x}"
x = x - 1
end
puts 'Done'
</code></pre>
</section>
<section>
<h3>While Loops</h3>
<pre><code class="ruby">
x = 10
while x > 0
puts "Loop number #{x}"
x = x - 1
end
</code></pre>
<p>The while statement takes a condition, and as long as it evaluates to true, the code block beneath it is repeated. This creates a <strong>loop</strong>.</p>
<p> Without the `x = x - 1` statement, to increment the value of x, this would be an <strong>infinite loop</strong> :( :( :(</p>
</section>
<section>
<h3>While loops</h3>
<p>Consider the following example that uses a while loop to sing you a song.</p>
<pre><code class="fragment ruby">
num_bottles = 99
while num_bottles > 0
puts "#{num_bottles} bottles of beer on the wall,
#{num_bottles} bottles of beer, take one down, pass it
around, #{num_bottles - 1} bottles of beer on the wall!"
num_bottles = num_bottles - 1
end
</code></pre>
<p>"#{num_bottles}" is an example of <strong>string interpolation</strong></p>
</section>
<!-- Let's Develop It - 10 minutes -->
<section>
<h3>Let's Develop It</h3>
<ul>
<li>Write a program that obtains user input like the last program</li>
<li>This program should not exit until the user says it should (maybe by entering "quit"?)</li>
<li>Use a loop!</li>
<li>You can use the next slide as an example.</li>
</ul>
</section>
<section>
<h3>Let's Develop It: Example</h3>
<pre><code>
# loopy.rb
loopy = true
while loopy == true
puts "Are we having fun yet?"
puts "Answer 'true' or 'false'."
user_input = gets.chomp
if user_input == 'false'
loopy = false
end
end
</code></pre>
<p>Learn more about loops in Ruby <a href="http://www.tutorialspoint.com/ruby/ruby_loops.htm" alt="Loops tutorial">here</a>.</p>
</section>
<section>
<h3>Each loops</h3>
<p>The most commonly used type of loop in Ruby is an each loop. It uses the <strong>.each</strong> method to iterate over a collection of elements, doing work to each one.</p>
<p>First, we need a collection. We use a <strong>range</strong> of numbers to loop over.</p>
<pre><code class="fragment ruby">
(0..5).each do |i|
puts "Value of i is #{i}"
end
</code></pre>
</section>
<section>
<h3>Each loops</h3>
<pre><code class="ruby">
(0..5).each do |i|
puts "Value of i is #{i}"
end
</code></pre>
<p>The loop has three parts:</p>
<ul>
<li>The collection that will be looped through, in this case a range- "(0..5)"</li>
<li>The name to give each element when the loop begins again - "i" - in the pipes "| |" </li>
<li>The code to execute with the element - the puts statement</li>
</ul>
<p>We will revisit the each loop when we have a better understanding of collections.</p>
</section>
<!-- Block 3 30 minutes -->
<section>
<h3>Collections</h3>
<p>There are three main types:</p>
<ul>
<li>Ranges</li>
<li>Arrays</li>
<li>Hashes</li>
</ul>
<pre><code class="fragment ruby">
new_range = (1..10)
new_array = [1, 3, 5]
new_hash = {"dog" => "snoopy", "bird" => "woodstock"}
</code></pre>
</section>
<section>
<h3>Ranges</h3>
<pre><code class="ruby">
inclusive_range = (1..3) # contains 1, 2, 3
exclusive_range = (1...3) # contains 1, 2
letter_range = ('a'..'e') # contains 'a', 'b', 'c', 'd', 'e'
</code></pre>
<p>Ranges are simply the range of values between the given first and last elements.</p>
<p><strong>Inclusive</strong> ranges have two dots, and include the last element. <strong>Exclusive</strong> ranges have three dots, and do not include the last element.</p>
<!--TODO is this right?-->
<p>Ranges need to be defined from lowest value to highest.</p>
</section>
<section>
<h3>Ranges</h3>
<p>Try out these range methods in IRB.</p>
<pre><code>
(1..99).max
('b'...'z').include?('j')
(890..902).begin
(890..902).first(4)
(890..902).last(3)
(890..902).end
(28..22).min
('a'...'g').each do |l|
puts "#{l} is a pretty good letter"
end
(22..28).to_a
</code></pre>
<p>Learn more about ranges <a href="http://www.ruby-doc.org/core-2.1.1/Range.html" alt="Ruby Doc">here</a>.</p>
</section>
<section>
<h3>Arrays</h3>
<p>Arrays have square brackets and can be filled with any type of object: integers, floats, strings, even other arrays or hashes.</p>
<pre><code class="fragment ruby">
new_array = [1, 3, 5, 89, 212, 7, -100]
arr = ["wow", "woooo", "zowie"]
array = Array.new #will have no elements inside it initially
varied_array = ["one", 2, "THREE", 0.4, ["five", 6]]
# methods to get information about an array
new_array.length
new_array.count
arr.include?("yee ha")
</code></pre>
<p>Arrays are a great way to keep track of information that changes frequently.</p>
</section>
<section>
<h3>Accessing Elements in an Arrays</h3>
<p>Arrays are <strong>ordered</strong> and are <strong>integer-indexed</strong>, starting at 0. </p>
<p>Elements can be accessed by their position.</p>
<pre><code class="fragment ruby">
new_array = [1, 3, 5, 89, 212, 7, -100]
arr = ["wow", "woooo", "zowie"]
new_array[0] # returns the zeroth element
arr[2] # returns the third element
arr[-1] # returns the last (1st from the end) element
new_array.last # returns the last element
new_array[1..2] # returns the second and third elements
arr.first # returns the first element
</code></pre>
</section>
<section>
<h3>Adding & Deleting From Arrays</h3>
<p>Adding and removing items to an array can be done in a variety of ways. These are the most common.</p>
<pre><code class="ruby">
arr = ["wow", "woooo", "zowie"]
#add
arr.push("hot diggity") # adds argument as last element
arr << "yikes" # adds argument as last element
#remove
arr.delete("wow") # deletes the element that matches argument
arr.pop # removes and returns the last element
</code></pre>
</section>
<section>
<h3>More Array Methods</h3>
<p>Arrays are used a lot in Ruby. There are a lot of cool methods available for them. </p>
<pre><code class="fragment ruby">
arr = ["dog", "cat", "turtle", "parakeet", "ferret"]
arr.index("dog") # returns the index of the element that matches argument
arr.join # returns a string made up of all the elements
arr.clear # removes all elements from the array
arr.reverse # returns new array with same elements, reversed
arr.shuffle # returns new array with same elements, shuffled
arr.uniq # returns a new array with only unique elements
arr.size # returns the number of elements in the array
arr.empty? # returns a boolean
</code></pre>
<p>Learn more about arrays <a href="http://www.ruby-doc.org/core-2.1.0/Array.html" alt="ruby documentation - array class">here</a>.</p>
</section>
<!-- minutes-->
<section>
<h3>Hashes</h3>
<p>Hashes have curly braces and hash rockets and can be filled with any data type: integers, floats, strings, even arrays and hashes. </p>
<pre><code class="fragment ruby">
grades_hash = { "Jane Doe" => 10, "Jim Doe" => 6, "Jan Doe" => 8}
new_hash = { 1 => "a", "d" => 12, "f" => 35 }
# methods to find information about hashes
new_hash.length
grades_hash.count
grades_hash.size
grades_hash.has_key?("Jan Doe")
new_hash.has_value?(35)
</code></pre>
<p>Syntax:</p>
<p>{ key => value, key => value }
</section>
<section>
<h3>Accessing Elements in Hashes</h3>
<p>Hashes are <strong>unordered.</strong> Hashes are like dictionaries, with unique <strong>key / value</strong> pairs.</p>
<p>Because hashes can have any type of object as an idex, and are unordered, we must access values by their <strong>key</strong>.</p>
<pre><code class="fragment ruby">
grades_hash = { "Jane Doe" => 10, "Jim Doe" => 6, "Jan Doe" => 8}
new_hash = { 1 => "a", "d" => 12, "f" => 35 }
grades_hash["Jane Doe"] # returns 10, the value of this key
new_hash["d"] # returns 12, the value of this key
grades_hash.first # returns first key/value pair... probably
</code></pre>
</section>
<section>
<h3>Adding & Removing from Hashes</h3>
<pre><code class="ruby">
new_hash = { 1 => "a", "d" => 12, "f" => 35 }
# add
new_hash["z"] = 43 # adds a new key/value pair "z" => 43
#remove
new_hash.delete("d") # removes key/value pair with specified key
new_hash.clear # removes all key/value pairs
</code></pre>
</section>
<section>
<h3>More Hash methods</h3>
<pre><code class="ruby">
chapters = {"My Early Home" => (1..15), "The Hunt" => (16..28),
"My Breaking In" => (29..46), "Birtwick Park" => (46..60)}
chapters.count # returns number of key/value pairs in hash
chapters.keys # returns an array of all the keys in hash
chapters.has_key?("How It Ended") # returns a boolean
chapters.to_a # converts hash to an array of arrays
chapters.invert # returns new hash with old one's values
# as keys and keys as values
</code></pre>
<p>Learn more about hashes <a href="http://www.ruby-doc.org/core-2.1.1/Hash.html" alt="Ruby Docs">here</a>.</p>
</section>
<section>
<h3>Enumerable</h3>
<p><strong>Arrays</strong> and <strong>Hashes</strong> are both members of the <strong>Enumerable</strong> class. There are a lot of cool methods available for Enumerable, including <strong>each</strong>. </p>
<!-- <p>Learn more about the methods available to Enumerable <a href="http://www.ruby-doc.org/core-2.1.1/Enumerable.html" alt="Ruby Docs">here</a>.</p> -->
</section>
<section>
<h3>.each with Ranges</h3>
<p>This is the simplest!</p>
<pre><code class="ruby">
(3..8).each do |n|
puts n * 4
end
</code></pre>
</section>
<section>
<h3>.each with Arrays</h3>
<p>Can be simple or more complex, depending on the array.</p>
<pre><code class="ruby">
pets_array = ["dog", "cat", "turtle", "parakeet", "ferret"]
pets_array.each do |p|
puts "I like #{p}s!!"
end
deep_array = [["mountain", "desert"], ["ocean", "sky"]]
deep_array.each do |p|
puts "I like #{p.first}s!!" # each element is also an array
end
</code></pre>
</section>
<section>
<h3>.each with Hashes</h3>
<p>Each element has a key and value that needs to be dealt with.</p>
<pre><code class="ruby">
grades_hash = { "Jane Doe" => 10, "Jim Doe" => 6, "Jan Doe" => 8}
grades_hash.each do |key, value|
puts "#{key}'s grade is #{value}"
end
</code></pre>
</section>
<!-- Let's develop it: 10 minutes -->
<section>
<h3>Let's Develop It</h3>
<p>Write a program that prints out every number between 1 and 1000 that is divisible by 7.</p>
<br />
<p>Hint: the modulo operator, %, will be helpful.</p>
</section>
<section>
<h3>Enumerable</h3>
<p>Visit <a href="https://gist.github.com/cherimarie/11004115" alt="Gist with pets array">this page</a> and copy the contents of the Gist to a local file. Save it as pets.rb. We'll work with it together in IRB.</p>
</section>
<section>
<h3>Enumerable: Reduce</h3>
<p>Returns the product of running the operator on all elements of the enumerable.</p>
<pre><code class="ruby">
(1..4).reduce(:*) # returns 1 * 2 * 3 * 4
(1...5).reduce(:+) # returns 1 + 2 + 3 + 4
(2...5).reduce(:**) # returns 2 ** 3 ** 4
</code></pre>
</section>
<section>
<h3>Enumerable: Collect and Map</h3>
<p>Returns an array with the results of running the block on each element. Can be used interchangably.</p>
<pre><code class="ruby">
$pets.collect{|p| p[:name]} # returns array of all pet names
$pets.collect{|p| p[:legs]}.reduce(:+) # returns sum of all pet legs
</code></pre>
</section>
<section>
<h3>Enumerable: Reject</h3>
<p>Returns an array with all elements that did not meet the critera in code block.</p>
<pre><code class="ruby">
$pets.reject{|p| p[:talents].include? "napping" }
# returns array of pets whose talents do not include napping
</code></pre>
</section>
<section>
<h3>Let's Develop It</h3>
<p>How many of our pets are nocturnal?</p>
</section>
<section>
<h3>Let's Develop It- Sample Code</h3>
<p>How many of our pets are nocturnal?</p>
<pre><code class="ruby">
$pets.reject{|p| p[:nocturnal]== false}.count
</code></pre>
</section>
<!--
<section>
<h3>Nil</h3>
<p class="fragment">Nil is an <strong>object</strong>! Try the following in IRB:</p>
<pre><code class="fragment ruby">
nil.class
nil.to_a
nil.to_i
nil.to_s
nil.size
</code></pre>
<p class="fragment">There are some methods associated with nil, like .to_a, to help prevent errors in your code. If you try to call .to_a on something without first setting the value of it, you'll get an empty array instead of an error.</p>
<p>Learn more about the nil class <a href="http://www.ruby-doc.org/core-2.1.0/NilClass.html" alt="ruby documentation - nil class">here</a>.</p>
</section> -->
<section>
<h3>Questions?</h3>
</section>
<section>
<h3>Homework</h3>
<p><strong>Practice:</strong> Find two interesting methods for Enumerable (via <a href="http://www.ruby-doc.org/core-2.1.1/Enumerable.html" alt="Ruby Docs">Ruby Docs</a>) and write a little program that uses them for arrays or hashes. Do any one the exercises at the end of <a href="http://pine.fm/LearnToProgram/?Chapter=06" alt="Chp 6 of Learn to Program">Chapter 6</a> of Learn to Program.</p>
<p><strong>Prep:</strong> Read <a href="http://pine.fm/LearnToProgram/?Chapter=08" alt="Chp 8 of Learn to Program">Chapter 8</a> of Learn To Program- don't try to do the exercises at the end yet, though.</p>
</section>
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