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<!DOCTYPE html>
<html>
<head>
<title>Ladies Learning Ruby</title>
<meta charset='utf-8'>
<script src='default.js'></script>
</head>
<style>
</style>
<body style='display: none'>
<section class='slides layout-regular template-default'>
<img src='images/ladieslearningcode-125x125.gif'>
<article>
<h1>
Learning to Program
<br>
with Ruby
</h1>
<p>
Dessy Daskalov
<br>
@dess_e
</p>
</article>
<article id="what-is-ruby">
<style>
#what-is-ruby p { margin: 100px 0px; font-size: 40px; line-height: 50px; };
</style>
<h3>
What is Ruby?
</h3>
<p />
<div class="build">
<p class='large-font'>Ruby is a programming language.</p>
<p class='large-font'>Wait ... what's a programming language?</p>
<p class='large-font'>Let's backtrack a bit.</p>
</div>
</article>
<article id='two-things'>
<style>
#two-things p { margin: 200px 0px; }
</style>
<p class='large-font'>There are two things you should know about your computer.</p>
</article>
<article id='computer-wishes'>
<style>
#computer-wishes h3 { padding-bottom: 10px; }
#computer-wishes img { margin-left: 70px; }
</style>
<h3>
1. Your computer speaks a different language.
</h3>
<p>This is how your computer wishes you could speak to it:</p>
<p />
<img src="images/machine-language.jpg" width="600" height="411" border="1">
</article>
<article>
<h3>
This is where a programming language comes in.
</h3>
<p>A programming language is a language that is relatively easy for you to learn, but can also be understood by the computer.</p>
<p>It's the middle ground between English and the language that the computer understands.</p>
</article>
<article id='stupid-computer'>
<style>
#stupid-computer p { margin: 200px 0px; }
</style>
<h3>
2. Your computer is not very smart.
</h3>
<p class='large-font'>Your computer can only do what you tell it to if you give it exact instructions.</p>
</article>
<article>
<h3>People vs. Computers</h3>
<p>
Suppose you had to teach a person how to make a peanut butter sandwich.
You might give the person an easy to follow recipe.
</p>
<p>1. Toast two slices of bread</p>
<p>2. Spread peanut butter on one slice of bread</p>
<p>3. Spread jam on the other slice of bread</p>
<p>4. Put the two pieces of bread together</p>
<p>5. Put the sandwich on a plate and serve it</p>
</article>
<article>
<h3>People understand GENERAL instructions.</h3>
<p>
We left out some parts of the process, but a person could figure out:
</p>
<p>Where to find the ingredients</p>
<p>To use a butter knife to spread the peanut butter</p>
<p>To put the bread in a toaster in order to toast it</p>
<p>etc, etc, etc (there are many little steps)</p>
</article>
<article id='computers-exact'>
<style>
#computers-exact p { margin: 150px 0px; };
</style>
<h3>Computers understand EXACT instructions.</h3>
<p class='large-font'>
This same recipe for a computer would be much, much longer.
</p>
</article>
<article>
<h3>1. Toast two slices of bread</h3>
<p>What is bread?</p>
<p>Where is it found?</p>
<p>How do I open the bag?</p>
<p>What is a slice?</p>
<p>How do I slice the bread?</p>
<p>How do I "toast"?</p>
<p>What is a toaster?</p>
<p>How do I use a toaster?</p>
<p>etc, etc, etc</p>
</article>
<article>
<h3>2. Spread peanut butter on one slice of bread</h3>
<p>What is peanut butter?</p>
<p>How do I "spread" peanut butter?</p>
<p>What is a butter knife?</p>
<p>Where is it found?</p>
<p>How do I open the knife drawer?</p>
<p>Which slice do I spread it on?</p>
<p>How much peanut butter do I spread?</p>
<p>etc, etc, etc</p>
</article>
<article id='programming-languages'>
<style>
#programming-languages p { margin-top: 80px; }
#programming-languages .mixed-font { line-height: 50px; }
#programming-languages b { font-size: 40px; }
</style>
<h3>Back to programming languages.</h3>
<p>A programming language makes it easier for you to give the computer instructions.</p>
<p class='mixed-font'>
It's made up of <b>simple elements</b>, that when <b>combined together</b>,
are used to write a set of <b>instructions</b> that the computer then breaks down and interprets as its own language.
</p>
</article>
<article id='learned-programming'>
<style>
#learned-programming p { margin-top: 100px; }
</style>
<h3>
You've just learned what programming is!
</h3>
<p class='large-font'>Programming is writing out <b>exact instructions</b> that your computer can follow to do things.</p>
</article>
<article id='ruby-rocks'>
<style>
#ruby-rocks .large-font { margin: 50px; }
</style>
<h3>
Why Ruby Rocks!
</h3>
<p>Created in 1993 by Yukihiro Matsumoto, from Japan.</p>
<p class='large-font'>
"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."
</p>
<p>Ruby is <b>fun</b>, it's <b>easy to learn</b>, and the <b>syntax is very forgiving</b>.</p>
</article>
<article>
<p class='large-font'>This is some code in Java:</p>
<section>
<pre>
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;
}
}</pre>
</section>
</article>
<article>
<p class='large-font'>The equivalent code in Ruby looks like this:</p>
<section>
<pre>
class Person
attr_accessor :name, :age
end
</pre>
</section>
</article>
<article id='irb-intro'>
<style>
#irb-intro .instructions { margin-top: 100px; }
</style>
<h3>
Time to see Ruby in action!
</h3>
<p>IRB is like text messaging with Ruby.</p>
<p>You'll ask Ruby to do something, and it will respond.</p>
<div class='instructions'>
<p><b>OS X</b></p>
<section>
<pre>Applications -> Utilities -> Terminal</pre>
</section>
<p />
<p><b>Windows</b> (C:\windows\system32\cmd.exe)</p>
<section>
<pre>Start -> All Programs -> Accessories -> Command Prompt</pre>
</section>
</div>
</article>
<article id='ask-ruby'>
<style>
#ask-ruby .large-font { margin-top: 100px; }
</style>
<section class='build'>
<pre>irb</pre>
<pre>ruby-1.9.2-p290 :001 > </pre>
<p class='large-font'>Let's ask Ruby to do something.</p>
</section>
</article>
<article>
<section class='build'>
<pre>> 1 + 1</pre>
<pre>=> 2</pre>
<pre>> 462 * 86</pre>
<pre>=> 39732</pre>
<p class='large-font'>Ruby can do math, and it can do it much quicker than a person can.</p>
</section>
</article>
<article id='ruby-knows'>
<style>
#ruby-knows .large-font { margin-top: 100px; }
</style>
<section class='build'>
<pre>> 1 + 2 + 3<br>=> 6</pre>
<pre>> "ladies" + "learning" + "code"</pre>
<pre>=> "ladieslearningcode"</pre>
<p class='large-font'>Ruby knows the difference between a number and a word.</p>
</section>
</article>
<article id='integer-string'>
<style>
#integer-string .ruby-class { margin: 100px 0px; }
</style>
<h3>
Numbers and Words, Integers and Strings
</h3>
<p>In Ruby ...</p>
<p class='ruby-class'>Numbers without decimals are called <b>INTEGERS</b>. We just did some math with some integers.</p>
<p class='ruby-class'>Letters, words, and sentences are called <b>STRINGS</b>. We tell Ruby that we are intending to use a string by wrapping it in quotes.</p>
</article>
<article id='objects-objects'>
<style>
#objects-objects .large-font { margin: 150px 0px; }
</style>
<h3>
Objects, Objects, Everywhere!
</h3>
<p>You've already met Objects. That's a programming word!</p>
<div class='build'>
<p class='large-font'>Everything in Ruby is an Object.</p>
</div>
</article>
<article id='classes-galore'>
<style>
#classes-galore .build { margin-top: 40px; }
#classes-galore .large-font { margin: 70px 0px; }
</style>
<h3>Classes</h3>
<div class='build'>
<p>Ruby is extremely picky and needs to classify everything before it knows what to do with it.<br>Ruby knows that ...</p>
<p class='large-font'>The number <b>1</b> is an <b>Integer</b>.
<p class='large-font'>The word <b>"ladies"</b> is a <b>String</b>.
<p>Integers and Strings are classes in Ruby. That's another programming word!</p>
</div>
</article>
<article>
<h3>City</h3>
<div class='class-diagram'>
<img src="images/toronto.png">
<img src="images/london.jpg">
<br>
<img src="images/new-york.jpg">
<img src="images/paris.jpg">
</div>
</article>
<article id='city-instance'>
<style>
#city-instance p { margin: 70px 0px; }
</style>
<div class='build'>
<p class='large-font'>Toronto is an instance of the class City.</p>
<p class='large-font'>London is an instance of the class City.</p>
<p class='large-font'>New York is an instance of the class City.</p>
<p class='large-font'>Paris is an instance of the class City.</p>
</div>
</article>
<article id='string-class'>
<style>
#string-class div { padding: 20px; }
</style>
<h3>String</h3>
<div class='class-diagram'>
"ladies"<br><br>
"ladieslearningcode"<br><br>
"The dog jumped over the fence."
</div>
</article>
<article id='string-instance'>
<style>
#string-instance p { margin: 70px 0px; }
</style>
<div class='build'>
<p class='large-font'>"ladies" is an instance of the class String.</p>
<p class='large-font'>"ladieslearningcode" is an instance of the class String.</p>
<p class='large-font'>"The dog jumped over the fence." is an instance of the class String.</p>
</div>
</article>
<article>
<h3>
Playing with Integers
</h3>
<section class='build'>
<pre>> 99.next</pre>
<pre>=> 100</pre>
<pre>> 99.odd?</pre>
<pre>=> true</pre>
<pre>> 99.even?</pre>
<pre>=> false</pre>
</section>
</article>
<article>
<h3>
Simple String Manipulation
</h3>
<section class='build'>
<pre>> "ladieslearningcode".capitalize</pre>
<pre>=> "Ladieslearningcode"</pre>
<pre>> "ladieslearningcode".upcase</pre>
<pre>=> "LADIESLEARNINGCODE"</pre>
<pre>> "ladieslearningcode".reverse</pre>
<pre>=> "edocgninraelseidal"</pre>
</section>
</article>
<article id='ruby-method'>
<style>
#ruby-method .large-font { margin: 60px 0px; }
</style>
<h3>
Methods
</h3>
<div class='build'>
<p class='large-font'><b>next</b>, <b>odd?</b>, and <b>even?</b> are all methods that you can call on an Integer.</p>
<p class='large-font'><b>capitalize</b>, <b>upcase</b>, and <b>reverse</b> are all methods that you can call on a String.</p>
<p class='large-font'>Methods are actions.</p>
</div>
</article>
<article id='class-methods'>
<style>
#class-methods .large-font { margin: 200px 0px; }
</style>
<p class='large-font'>Classes come packaged with methods.</p>
</article>
<article>
<h3>
I'm lazy! I don't want to do all of this typing!
</h3>
<p>What if we could type in "ladieslearningcode" just once, and store it for later use? We can!</p>
<section>
<pre>> llc = "ladieslearningcode"</pre>
<pre>=> "ladieslearningcode"</pre></section>
<p>You've just <b>assigned</b> the String "ladieslearningcode to the <b>variable</b> llc.</p>
<p>A programmer would say that the variable llc points to the object "ladieslearningcode".</p>
</article>
<article>
<h3>
Variables Can (And Often Do!) Vary
</h3>
<p>A variable is called just that because the object it points to can change.</p>
<section class='build'>
<pre>> llc = "a lady learning code"</pre><pre>=> "a lady learning code"</pre>
<div>llc <img src='images/arrow.png'> "a lady learning code"</div>
<p>Now let's ask for the value of llc.</p>
<pre>> llc</pre><pre>=> "a lady learning code"</pre>
</section>
</article>
<article>
<p>Let's try some more</p>
<section class='build'>
<pre>> llc = 99</pre><pre>=> 99</pre>
<div>llc <img src='images/arrow.png'> 99</div>
<p>Let's ask for the value of llc once again.</p>
<pre>> llc</pre><pre>=> 99</pre>
</section>
</article>
<article>
<h3>The More the Merrier</h3>
<p>Let's introduce another variable.</p>
<section class='build'>
<pre>> copy_cat = llc</pre><pre>=> 99</pre>
<div>llc <img src='images/arrow.png'> 99 <img src='images/back-arrow.png'> copy_cat</div>
</section>
</article>
<article>
<p>Let's ask for the value of each variable.</p>
<section class='build'>
<pre>> llc</pre><pre>=> 99</pre>
<pre>> copy_cat</pre><pre>=> 99</pre>
<p>Now set llc back to "ladieslearningcode"</p>
<pre>> llc = "ladieslearningcode"</pre><pre>=> "ladieslearningcode"</pre>
</section>
</article>
<article>
<h3>
String Manipulation With Our Variable
</h3>
<p>You can now use this variable exactly like you would have used "ladieslearningcode" before.</p>
<section>
<pre>> llc.capitalize</pre>
<pre>=> "Ladieslearningcode"</pre>
<pre>> llc.upcase</pre>
<pre>=> "LADIESLEARNINGCODE"</pre>
<pre>> llc.reverse</pre>
<pre>=> "edocgninraelseidal"</pre>
</section>
</article>
<article>
<h3>Modifying the value with a method</h3>
<section class='build'>
<pre>> llc.reverse</pre><pre>=> "edocgninraelseidal"</pre>
<p>Try asking for the value of llc now.</p>
<pre>> llc</pre><pre>=> "ladieslearningcode"</pre>
</section>
</article>
<article id='wait-why'>
<style>
#wait-why p { margin: 50px 0px; }
</style>
<h3>Wait. Why didn't it change?</h3>
<section class='build'>
<p class='large-font'>llc is still pointing to "ladieslearningcode". You didn't tell it to point to a different string.</p>
<div>llc <img src='images/arrow.png'> "ladieslearningcode"</div>
<p class='large-font'>If you want the value to change, you have to set it to something else.</p>
</section>
</article>
<article>
<section class='build'>
<pre>> llc = llc.reverse</pre><pre>=> "edocgninraelseidal"</pre>
<pre>> llc</pre><pre>=> "edocgninraelseidal"</pre>
<p class='large-font'>If you want the value of a variable to change, you have to explicitly tell it to change.</p>
</section>
</article>
<article>
<h3>
Let's Try One More
</h3>
<div class='build'>
<pre>> llc.length</pre>
<pre>=> 18</pre>
<p class='large-font'>
You're probably starting to get a sense of how Twitter knows
how many characters you've typed in.
</p>
</div>
</article>
<article>
<h3>Doing like Twitter does.</h3>
<section class='build'>
<pre>> tweet = "I'm writing my first program at the @llcodedotcom<br>Intro to Ruby workshop!"</pre>
<pre>=> "I'm writing my first program at the @llcodedotcom <br>Intro to Ruby workshop!"</pre>
<pre>> tweet.length</pre>
<pre>=> 73</pre>
<p class='large-font'>We now know enough to write a program.</p>
</section>
</article>
<article>
<h3>
Writing Our First Program
</h3>
<p>
Open any text editor, add the same code, and save it as twitter.rb in your llc directory.
</p>
<section>
<pre>tweet = "I'm writing my first program at the @llcodedotcom<br>Intro to Ruby workshop!"<br>tweet.length</pre>
</section>
<p>To run your program, type <b>quit</b> to exit from IRB, and then type:</p>
<section>
<pre>ruby twitter.rb</pre>
</section>
<div class='build'><p>Wait, what? Why didn't it show me the length of my string?</p></div>
</article>
<article id='ruby-output'>
<style>
#ruby-output .large-font { margin: 50px 0px; }
</style>
<h3>
Outputting Text to the Screen
</h3>
<p class='large-font'>IRB is like back-and-forth text messaging.</p>
<p class='large-font'>A program has to be told when to output something</p>
<p>Modify your program:</p>
<section>
<pre>tweet = "I'm writing my first program at the @llcodedotcom<br>Intro to Ruby workshop!"<br>puts tweet.length</pre>
</section>
</article>
<!-- just words, highlight in a different colour before -->
<article id='recap-one'>
<style>
#recap-one .large-font { margin: 50px 0px; text-align: center; }
</style>
<h3>
Recap Slide
</h3>
<div class='build'>
<p class='large-font'>Integer</p>
<p class='large-font'>String</p>
<p class='large-font'>Class</p>
<p class='large-font'>Object</p>
<p class='large-font'>Variable</p>
</div>
</article>
<article id='puzzle-one'>
<style>
#puzzle-one .large-font { margin: 100px 0px; }
</style>
<h3>
Puzzle One - Variables
</h3>
<p class='large-font'>Open puzzle_1.rb in the puzzles folder, and write down the output you expect to see if you were to run this script.</p>
<p class='large-font'>If you're not sure of something, remember that you can type <b>irb</b> again and try it out.</p>
</article>
<article id='real-twitter'>
<style>
#real-twitter .large-font { margin: 60px 0px; }
</style>
<h3>
Getting Input From the User
</h3>
<p>The real Twitter...</p>
<div class='build'>
<p class='large-font'>Asks you to type something.</p>
<p class='large-font'>Tells you how many characters you're working with.</p>
<p>So far, we've just been putting our tweet directly into the program.</p>
</div>
</article>
<article>
<h3>
Asking for Input
</h3>
<p>The <b>puts</b> method is used for output, and the <b>gets</b> method is used for input. Try this:</p>
<p>The gets method warns Ruby that you're about to speak.</p>
<section class='build'>
<pre>> tweet = gets</pre>
<pre class='all-string'>I'm learning Ruby with #ladieslearningcode</pre><pre>=> "I'm learning Ruby with #ladieslearningcode\n"</pre>
<p>
Wait, we didn't type \n in our tweet. What is that?
</p>
</section>
</article>
<article>
<h3>
Asking for Input
</h3>
<p>
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:
</p>
<section class='build'>
<pre>> tweet = gets.chomp</pre>
<pre class='all-string'>I'm learning Ruby with #ladieslearningcode</pre>
<pre>=> "I'm learning Ruby with #ladieslearningcode"</pre>
</section>
</article>
<article>
<h3>
Asking for Input
</h3>
<p>Now try this:</p>
<section class='build'>
<pre>> tweet = gets.chomp</pre>
<pre class='all-string'>I'm a lady learning code with @llcodedotcom #ladieslearningcode</pre>
<pre>=> "I'm a lady learning code with @llcodedotcom #ladieslearningcode"</pre>
<pre>> puts tweet</pre>
<pre class='all-string'>I'm a lady learning code with @llcodedotcom #ladieslearningcode<br>=> nil</pre>
</section>
</article>
<article id='nil-nothing'>
<style>
#nil-nothing p { margin: 80px 0px; }
</style>
<h3>What's nil? It's nothing, don't worry.</h3>
<p>You asked Ruby to output your tweet, and Ruby did just that.</p>
<p>
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.
</p>
<p>nil is also an Object, and it just represents nothing.</p>
</article>
<article id='ask-for-tweet'>
<style>
#ask-for-tweet .build { margin-top: 60px; }
</style>
<h3>
Back to your Twitter Program
</h3>
<p>Working with your group, modify your Twitter program to do the following:</p>
<div class='build'>
<p>1. Ask (politely!) for a tweet from the user.</p>
<p>2. Store the tweet in a variable, without \n</p>
<p>3. Output the tweet the user gave.</p>
<p>4. Output the number of characters in the tweet.</p>
<p>5. Output how many <b>more</b> characters the user can add until they hit 140 characters.</p>
<p>(answers in assignments/twitter_3.rb)</p>
</div>
</article>
<article id='conditional-twitter-1'>
<style>
#conditional-twitter-1 .large-font { margin-top: 100px; }
</style>
<h3>
Giving Output Based on Input
</h3>
<p>Twitter...</p>
<p class='large-font'>Lets you send your tweet if it is 140 characters or less</p>
<p class='large-font'>Tells you that your tweet is too long to send otherwise.</p>
</article>
<article id='conditional-twitter-2'>
<style>
#conditional-twitter-2 .large-font { margin-top: 100px; }
</style>
<h3>Giving Output Based on Input</h3>
<p class='large-font'>
So far we know how to determine the length of the user's tweet.
</p>
<p class='large-font'>
We don't know how to tell them
whether they can or cannot send their tweet, depending on it's length.
</p>
</article>
<article id='conditional-logic'>
<style>
#conditional-logic .large-font { margin-top: 100px; }
</style>
<h3>Conditional Logic</h3>
<p class='large-font'>Programming is writing out sets of simple instructions for the computer to follow.</p>
<p class='large-font'>Let's break down out tweet logic into simple instructions.</p>
</article>
<article id='conditional-instructions'>
<style>
#conditional-instructions .large-font { margin-top: 80px; }
</style>
<h3>
Conditional Logic
</h3>
<p>We want our program to ...</p>
<p class='large-font'>if the tweet is greater than 140 characters, tell the user that they cannot send their tweet</p>
<p class='large-font'>if the tweet is less than or equal to 140 characters, tell the user that they can send their tweet</p>
</article>
<article id='greater-than'>
<style>
#greater-than .large-font { margin: 100px 0px; }
</style>
<h3>
Conditional Logic: Greater Than
</h3>
<p class='large-font'>The math symbol for <b>greater than</b> is <b>></b></p>
<p>Try the code below in IRB:</p>
<section class='build'>
<pre>> 200 > 140</pre><pre>=> true</pre>
</section>
</article>
<article>
<h3>
Conditional Logic: Greater Than
</h3>
<p>Now try:</p>
<section class='build'>
<pre>> number_of_characters = 200</pre><pre>=> 200</pre>
<pre>> number_of_characters > 140</pre><pre>=> true</pre>
</section>
</article>
<article>
<h3>
Conditional Logic: Greater Than
</h3>
<p>Now try:</p>
<section class='build'>
<pre>> number_of_characters = 80</pre><pre>=> 80</pre>
<pre>> number_of_characters > 140</pre><pre>=> false</pre>
</section>
</article>
<article id='less-than'>
<style>
#less-than .large-font { margin: 50px 0px; }
</style>
<h3>
Conditional Logic: Less Than
</h3>
<p class='large-font'>The math symbol for <b>less than</b> is <b><</b></p>
<p>Try the code below in irb</p>
<section class='build'>
<pre>> llc = "ladieslearningcode"</pre><pre>=> "ladieslearningcode"</pre>
<pre>> llc.length < 140</pre><pre>=> true</pre>
</section>
</article>
<article id='conditional-logic'>
<h3>
Conditional Logic in Our Simple Twitter
</h3>
<p class='large-font'>Let's simplify our if statements.</p>
<p class='large-font'>Remember that we're storing the user's tweet in the variable tweet.</p>
</article>
<article id='conditional-simplify'>
<style>
#conditional-simplify p { margin: 50px 0px; }
</style>
<h3>
Conditional Logic in Our Simple Twitter
</h3>
<p>Original if statements:</p>
<p>if the tweet is greater than 140 characters, tell the user that they cannot send their tweet</p>
<p>if the tweet is less than 140 characters, tell the user that they can send their tweet</p>
<p />
<div class='build'>
<!-- split up, and put actual statement instead of crap code -->
<p>if tweet.length > 140 puts "Your tweet is too long!"</p>
<p>if tweet.length < 140 puts "Tweet your heart out!"</p>
</div>
</article>
<article>
<h3>
Try it out!
</h3>
<p>
Replace the puts statements in your Twitter program with the code below.
(see assignments/twitter_4.rb if needed)
</p>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>end<br><br>if tweet.length < 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p>
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?
</p>
</article>
<article id='conditional-instructions'>
<h3>
Your First Bug!
</h3>
<p class='large-font'>We're not actually taking into account all possible tweet lengths.</p>
<p class='large-font'>Programming problems can be solved many different ways.</p>
<p class='large-font'>We'll look at three different solutions.</p>
</article>
<article id='conditional-logic'>
<h3>
First (Worst) Solution
</h3>
<p class='large-font'>Since we're only missing one case, the case where the tweet is exactly 140 characters, we can just add another if statement.</p>
</article>
<article>
<h3>
First (Worst) Solution
</h3>
<p>Add this last if statement to the bottom of your file: (see assignments/twitter_5.rb if needed)</p>
<section>
<pre>if tweet.length == 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>
The == operator checks that the value of the objects on either side of it are equal.
</p>
</article>
<article id='conditional-logic'>
<h3>
Refactoring Our Code
</h3>
<p class='large-font'>
Programmers are always refactoring (re-strcturing, re-organizing) their code to make it cleaner and more readable.
Right now is a great time to do that.
</p>
</article>
<article>
<h3>
Refactoring Our Code
</h3>
<p>Three if statements are unnecessary. We can actually combine all of these if statements into one, like so:</p>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>elsif tweet.length < 140<br> puts "Tweet your heart out!"<br>elsif tweet.length == 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p>(see assignments/twitter_6.rb if needed)</p>
</article>
<article id='conditional-logic'>
<h3>if .. elsif</h3>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>elsif tweet.length < 140<br> puts "Tweet your heart out!"<br>elsif tweet.length == 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>In the above code, if the first statement doesn't evaluate to true, then the next one is attempted, and so on.</p>
</article>
<article id='conditional-logic'>
<h3>if .. elsif</h3>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>elsif tweet.length < 140<br> puts "Tweet your heart out!"<br>elsif tweet.length == 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>
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.
</p>
</article>
<article id='conditional-logic'>
<h3>if .. elsif</h3>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>elsif tweet.length < 140<br> puts "Tweet your heart out!"<br>elsif tweet.length == 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>If none of the statements evaluate to true, then none of the puts statements are executed.</p>
</article>
<article>
<h3>
Second Solution
</h3>
<p>Notice that the line puts "Tweet your hear out!" is unnecessarily repeated?</p>
<p>Let's cut it out by replacing the entire if statement with the code below:</p>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>elsif tweet.length <= 140<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p>(see assignments/twitter_7.rb if needed)</p>
</article>
<article id='conditional-instructions'>
<h3>Less than or equal to with <=, Greater than or equal to with >=</h3>
<p class='large-font'>The <b><=</b> operator checks for equality as well.</p>
<p class='large-font'>Checking for equality with greater than works exactly the same way, using the <b>>=</b> operator.</p>
</article>
<article>
<h3>
Third Time's a Charm
</h3>
<p>
This is better, but look at the logic closely. Do we really even need to specify the second condition?
</p>
<p>Replace your code again with the code below:</p>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>else<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p>(see assignments/twitter_8.rb if needed)</p>
</article>
<article id='conditional-logic'>
<h3>if .. else</h3>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>else<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>
Just like with if .. elsif, only one puts statement is ever executed. The difference here is that one of the
puts statements is <b>always</b> executed.
</p>
</article>
<article id='conditional-logic'>
<h3>if .. else</h3>
<section>
<pre>if tweet.length > 140<br> puts "Your tweet is too long!"<br>else<br> puts "Tweet your heart out!"<br>end</pre>
</section>
<p class='large-font'>
The else is there are a <b>catch-all</b>. 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.
</p>
</article>
<article>
<h3>Hello, Operator?</h3>
<table>
<tr><td>Operator</td><td>True</td><td>False</td></tr>
<tr>
<td>==</td>
<td>99 == 99</td>
<td>99 == 100</td>
</tr>
<tr>
<td>!=</td>
<td>99 != 100</td>
<td>99 != 99</td>
</tr>
<tr>
<td>></td>
<td>100 > 99</td>
<td>99 > 100</td>
</tr>
<tr>
<td><</td>
<td>99 < 100</td>
<td>100 < 99</td>
</tr>
<tr>
<td>>=</td>
<td>99 >= 99</td>
<td>99 >= 100</td>
</tr>
<tr>
<td><=</td>
<td>99 <= 99</td>
<td>100 <= 99</td>
</tr>
</table>
</article>
<article id='recap-two'>
<h3>Recap Slide</h3>
<style>
#recap-two .large-font { margin: 50px 0px; text-align: center; }