Table of Contents

JavaScript

  1. How We Got to Now
  2. In the Browser & On the Server
  3. Objects & Core Types
  4. Exercise: Practice Making Objects & Functions
  1. Expressions & Declarations
  2. Higher Order Functions
  3. Exercise: Array.prototype.sort
  4. Closures
  5. Exercise: Make an Accumulator
  6. Objects & Inheritance
  7. Exercise: Turducken
  1. Installation
  2. Using npm and the Node REPL
  3. Using `require` and `module`
  4. The Event Loop: The What and Why of Asynchronous Programming
  5. Exercise: Your First Webserver
  1. Installing Express
  2. Typical Structure of an Express Web Application
  3. Incorporating SQL: An Exercise in Asynchronous Patience
  4. Exercise: Port Sinatra to Express

Fundamentals of Programming

  1. Welcome to Ruby
  2. Core Data Types
  3. Iterators & Blocks
  4. Flow Control & Conditionals
Fundamentals of Programming Introduction to Ruby Flow Control & Conditionals

Ruby 104: Flow Control & Conditionals

Comparisons

Equality comparisons can be used on all objects, including Strings, Integers, Floats, Arrays, Hashes, etc: - == (equal to?) - != (not equal to?)

Numeric comparisons are used primarily on Integers and Floats: - > (greater than?) - < (less than?) - >= (greater than or equal to?) - <= (less than or equal to?)

The “result” of a comparison is known as a boolean. There are only two kinds of boolean object: - true - false

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1 > 0
# => true

"hello" == "hello"
# => true

Flow Control

Conditionals

if and else allow you to control the flow of your program. This means that they allow you to define which lines of code will execute, and which will be skipped.

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if boolean_value
  code
end

additional_code

When you use an if, the code that follows it (until the end) will only be executed if the boolean_value is true. Additionally, you may add else before the end:

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if boolean_value
  code
else
  other_code
end

additional_code

In this case, when boolean_value is false, then other_code will be executed. Otherwise, it will be skipped. When you have an if and an else only one or the other of code or other_code will be executed, and that is determined by the value of boolean_value.

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puts "Hey! What’s your name?"
response = gets.chomp

is_my_name = response.downcase == "computer"
if is_my_name
  puts "Weird, that's my name too. Small world!"
else
  puts "Wacky name!"
end

puts "Well, it was nice to meet you #{response}."

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if 1 > 0
  # do something
else
  # do something different
end

Negating Comparisons

Ruby has an unless keyword that works just like if, but in the reverse way.

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puts "What is your favorite animal?"
fav_animal = gets.chomp

if fav_animal.downcase == "camel"
  puts "I also love camels!"
else
  puts "That's a great animal, but I love camels the most."
end

# The following code works identically to the above
unless fav_animal.downcase == "camel"
  puts "That's a great animal, but I love camels the most."
else
  puts "I also love camels!"
end

The if block executes if the conditional evaluates as true. The unless block executes if the conditional evaluates as false.

Another way to “negate” a conditional is to use the ! (not) operator. This should be placed just before a boolean value, or a comparison. When combined with a comparison the comparison should be enclosed in parentheses:

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puts "What day of the week is it?"
day_of_week = gets.chomp

puts "What did you have for lunch today?"
lunch = gets.chomp

if day_of_week.downcase == "tuesday"
  if !(lunch == "tacos")
    puts "Taco Tuesdays are my favorite, though!"
  end
end

Compound Conditions

Comparisons are often combined. Combinations can take one of two forms, and and or. When you combine with and, both comparisons must be true for the entire combination to be true. By combining with or, when either of the comparisons are true, the entire combination is true: - && (and) - || (or)

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puts "What is your first name?"
first_name = gets.chomp
puts "What is your last name?"
last_name = gets.chomp

if first_name.length > 8
  if last_name.length > 10
    puts "Your name is considerable!"
  end
end

# This is the same as the above
if first_name.length > 8 && last_name.length > 10
  puts "Your name is considerable!"
end

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if command == "add"
  puts "We're adding numbers."
end

if command == "+"
  puts "We're adding numbers."
end

# This is the same as the above
if command == "add" || command == "+"
  puts "We're adding numbers."
end

Complex conditionals

The if/else/end code we’ve written above is the standard and simplest form of a conditional. It is possible to extend this form with one or more elsif lines:

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if command == "add" || command == "+"
  puts "We're adding numbers"
else
  if command == "subtract" || command == "-"
    puts "We're subtracting numbers"
  else
    if command == "multiply" || command == "*"
      puts "We're multiplying numbers"
    end
  end
end

# This is equivalent to the above
if command == "add" || command == "+"
  puts "We're adding numbers"
elsif command == "subtract" || command == "-"
  puts "We're subtracting numbers"
elsif command == "multiply" || command == "*"
  puts "We're multiplying numbers"
end

This can be very useful, when you have more than one elsif line, because the indentation, or nesting, can quickly become very deep, and more difficult to understand.

Simplifying really complex conditionals

When you have several elsif lines within a single if, there’s a way to write each conditional, with much less repetition:

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if command == "add" || command == "+"
  puts "We're adding numbers"
elsif command == "subtract" || command == "-"
  puts "We're subtracting numbers"
elsif command == "multiply" || command == "*"
  puts "We're multiplying numbers"
elsif command == "divide" || command == "/"
  puts "We're dividing numbers"
elsif command == "exponify" || command == "**"
  puts "We're exponentiating numbers"
elsif command == "sqrt"
  puts "We're finding the square root of a number"
else
  puts "What do you want from me?!"
end

The above code works, but it’s kinda messy. We can trim it by using the case/when syntax: ~~~ruby case command when “add”, “+” puts “We’re adding numbers” when “subtract”, “-“ puts “We’re subtracting numbers” when “multiply”, “*” puts “We’re multiplying numbers” when “divide”, “/” puts “We’re dividing numbers” when “exponify”, “**” puts “We’re exponentiating numbers” when “sqrt” puts “We’re finding the square root of a number” else puts “What do you want from me?!” end ~~~

Conditional Loops

### Wait a while Execute the iterator while the condition is true.

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i = 0

while i < 4
  puts i
  i += 1
end

The above code will output the values of i until i is no longer less than 4, resulting in the following output: ~~~ 0 1 2 3 ~~~

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command = gets.chomp

while command != "add" && command != "+"
  puts "Please tell me to add (+)!"
  command = gets.chomp
end

puts "OMG It's about time!"

Make it clearer by using Until

Execute the iterator until the condition is true.

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i = 0

until i == 4
   puts i
   i += 1
end

The above code will output the values of i until i is equal to 4, resulting in the following (equivalent to the above) output: ~~~ 0 1 2 3 ~~~

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command = gets.chomp

until command == "add" || command == "+" || command == "subtract" || command == "-"
  puts "Please tell me to add (+) or subtract (-)!"
  command = gets.chomp
end

puts "OMG It's about time!"

Make it clearer by using include?

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command = gets.chomp

until ["add", "+", "subtract", "-"].include? command
  puts "Please tell me to add (+) or subtract (-)!"
  command = gets.chomp
end

puts "OMG It's about time!"