Become a Ruby Professional

This module provides a thorough explanation of modern concepts for beginners. 
Beginners will get a refresher on Ruby. Those who’re already familiar with the language will rediscover object-oriented concepts, memory organization, find career advice, and save the planet from a nuclear apocalypse.
Let's tune in!

The Handbook for Ruby Developers

True or False: Ruby gems are libraries created by developers from around the world with useful functionality.

True or False: Ruby gems are libraries created by developers from around the world with useful functionality.

What's the result of the following program?
```ruby
arr = [
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9, 10, 11, 12]
]
puts arr[1][2] + arr[2][1]
```

What’s the result of the following program?
<pre><code class="language-ruby">arr = [
 [1, 2, 3, 4],
 [5, 6, 7, 8],
 [9, 10, 11, 12]
]
puts arr[1][2] + arr[2][1]
</code></pre>

Consider this three-dimensional array:
```ruby
arr = [
  [
    %w(a b c),
    %w(d e f),
    %w(g h i)
  ],
  [
    %w(aa bb cc),
    %w(dd ee ff),
    %w(gg hh ii)  
  ]
]
```
What is the result of following expression?
```ruby 
arr[0][0][1] + arr[1][1][1] + arr[0][1][2] 
```


Consider this three-dimensional array:
<pre><code class="language-ruby">arr = [
 [
 %w(a b c),
 %w(d e f),
 %w(g h i)
 ],
 [
 %w(aa bb cc),
 %w(dd ee ff),
 %w(gg hh ii) 
 ]
]
</code></pre>
What is the result of following expression?
<pre><code class="language-ruby">arr[0][0][1] + arr[1][1][1] + arr[0][1][2] 
</code></pre>

What is the result of `''.empty? `expression?


What is the result of <code>''.empty? </code>expression?

What is the result of `''.nil?` expression?

What is the result of <code>''.nil?</code> expression?

What is the result of the following expression?
```ruby
'HELLO'.size + %w(H E L L O).count { |x| x == 'L' }

What is the result of the following expression?
<pre><code class="language-ruby">'HELLO'.size + %w(H E L L O).count { |x| x == 'L' }</code></pre>

What is the result of the following expression?
```ruby
%w(H E L L O).include?('L')

What is the result of the following expression?
<pre><code class="language-ruby">%w(H E L L O).include?('L')</code></pre>

What is the result of the following expression? (Hint: Normally, the result of an expression is the result of the last statement; it is the last line on the screen once you paste the code below into your REPL.)
```ruby
arr = [1, 2, 3]
arr.push(4)
arr.inspect


What is the result of the following expression? (Hint: Normally, the result of an expression is the result of the last statement; it is the last line on the screen once you paste the code below into your REPL.)
<pre><code class="language-ruby">arr = [1, 2, 3]
arr.push(4)
arr.inspect
</code></pre>

What is the result of the following expression?
```ruby
arr = [1, 2, 3, 4]
arr.pop

What is the result of the following expression?
<pre><code class="language-ruby">arr = [1, 2, 3, 4]
arr.pop</code></pre>

What is the result of the following expression?
```ruby
arr = [1, 2, 3]
arr.unshift(4)
arr.inspect

What is the result of the following expression?
<pre><code class="language-ruby">arr = [1, 2, 3]
arr.unshift(4)
arr.inspect</code></pre>

What is the result of the following expression?
```ruby
arr = [4, 1, 2, 3]
arr.shift

What is the result of the following expression?
<pre><code class="language-ruby">arr = [4, 1, 2, 3]
arr.shift</code></pre>

What is the result of the following expression?
```ruby
arr = [1, 2, 3, 4]
arr.select { |x| x > 2 }

What is the result of the following expression?
<pre><code class="language-ruby">arr = [1, 2, 3, 4]
arr.select { |x| x &gt; 2 }</code></pre>

What is the result of the following expression?
```ruby
arr = [true, false, true, false, 1, 2, 3]
arr.reject { |x| x == false }

What is the result of the following expression?
<pre><code class="language-ruby">arr = [true, false, true, false, 1, 2, 3]
arr.reject { |x| x == false }</code></pre>

What is the result of the following expression?
```ruby
%w(B E N J A M I N).take(3)

What is the result of the following expression?
<pre><code class="language-ruby">%w(B E N J A M I N).take(3)</code></pre>

What is the result of the following expression?
```ruby
[0, 2, 3, 4, 5].any? { |element| element == 1 + 3 }

What is the result of the following expression?
<pre><code class="language-ruby">[0, 2, 3, 4, 5].any? { |element| element == 1 + 3 }</code></pre>

What is the result of the following expression?
```ruby
legal_age = 18
[17, 18, 19, 20, 21].all? { |age| age >= legal_age }

What is the result of the following expression?
<pre><code class="language-ruby">legal_age = 18
[17, 18, 19, 20, 21].all? { |age| age &gt;= legal_age }</code></pre>

Try to guess; what the result of the following expression would be.
```ruby
students = [
  { name: 'Sam', age: 17, class: :math, score: 5 },
  { name: 'Pat', age: 18, class: :arts, score: 10 },
  { name: 'Joe', age: 19, class: :math, score: 1 },
  { name: 'Ann', age: 20, class: :arts, score: 2 },
  { name: 'Lev', age: 21, class: :math, score: 3 }
]
students.select { |student| student[:age] >= 18 }.take(2).reject { |student| student[:class] == :math }[0][:name]

Try to guess; what the result of the following expression would be.
<pre><code class="language-ruby">students = [
 { name: 'Sam', age: 17, class: :math, score: 5 },
 { name: 'Pat', age: 18, class: :arts, score: 10 },
 { name: 'Joe', age: 19, class: :math, score: 1 },
 { name: 'Ann', age: 20, class: :arts, score: 2 },
 { name: 'Lev', age: 21, class: :math, score: 3 }
]
students.select { |student| student[:age] &gt;= 18 }.take(2).reject { |student| student[:class] == :math }[0][:name]</code></pre>

What is the result of the following expression?
```ruby
if 'blabla' == :blabla
  true
else
  false
end

What is the result of the following expression?
<pre><code class="language-ruby">if 'blabla' == :blabla
 true
else
 false
end</code></pre>

What is the result of the following expression?
```ruby
if 'blabla'.to_sym == :blabla
  true
else
  false
end

What is the result of the following expression?
<pre><code class="language-ruby">if 'blabla'.to_sym == :blabla
 true
else
 false
end</code></pre>

```ruby
[“1”, “100”, “30”, “20”]

What is the result of the `['1', '30', '20', '100'].sort` expression?

What is the result of the <code>['1', '30', '20', '100'].sort</code> expression?

What method do we use to iterate over an array?

What method do we use to iterate over an array?

Which of the following statements can initialize an empty array?

Which of the following statements can initialize an empty array?

What's the result of the following program?
```ruby
arr = [1,2,3,4,5,6,7,8,9]
puts arr[1] + arr[2] + arr[3]

What’s the result of the following program?
<pre><code class="language-ruby">arr = [1,2,3,4,5,6,7,8,9]
puts arr[1] + arr[2] + arr[3]</code></pre>

____ syntax is a quick way to define an array of strings in Ruby.

____ syntax is a quick way to define an array of strings in Ruby.

____ syntax is a quick way to define an array of symbols in Ruby.

____ syntax is a quick way to define an array of symbols in Ruby.

Take a quiz on arrays before moving onto the next chapter.

First Steps

Fundamentals of Ruby

Conditional Statements

Operators and Methods

Arrays

Hash

Fun with Object Oriented Programming

Debugging in Ruby

Ruby Version Manager

Testing Ruby Programs

Appendix

Conclusion

Quiz: Arrays