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Homework Discussion

How was last week's homework?

Do you have any questions or concepts that you'd like to discuss?

The Homework was:

• Ranges problem
• Pet shop
• Bye Grandma

HW: grandma.rb

            chatting = true
            byes = 0
            while chatting
              puts "Ask Grandma a question:"
              said = gets.chomp!
              if said == "BYE"
                byes += 1
                if byes > 2
                  chatting = false
                else
                  puts "** Grandma is ignoring you **"
                end
              elsif said == said.upcase
                year = 1930 + Random.rand(20)
                puts "NO, NOT SINCE #{year}!"
              else
                puts "HUH?!  SPEAK UP, SONNY!"
              end
            end
            puts "Thanks for chatting with Grandma"
              

Review

• Conditions - if, elsif, else
• Loops - while, for
• Arrays - [1,2,3]
• Ranges - [1..3]
• Hashes - {"one" => 1, "two" => 2}

What we will cover today

• Methods
• Objects
• Object Oriented Programming

Methods

A method is a name for a chunk of code

Methods are often used to define reusable behavior.

                        1.even?
                        => false

                        "fred".capitalize
                        => "Fred"
                        
                        "fred".class
                        => String
                        

If you have code you want to reuse or organize, methods will help.

Writing A Method

Just like with loops and conditionals there is a term used to declare a method, def and end

            def subtract(x, y)
              x - y
            end
            

def means define

subtract is the name of the method

x, y are parameters

x - y is the body of the method

x - y is also the return value

Calling A Method

Arguments are passed
and parameters are declared.

Note that the variable names don't have to match!

In this code, 5 is an argument and x is a parameter

              def subtract(x,y) #parameters
                x - y
              end

              subtract(5, 2) #arguments
            

Returning Values

Every Ruby method returns something.

Usually, it's the last statement in the method.

It could be the value sent to return if that came first.

            def subtract(x,y)
              x - y
              'another thing'
            end

            return_value = subtract(5, 2)
            puts return_value

            def subtract(x,y)
              return x - y
              'another thing'
            end

            return_value = subtract(5, 2)
            puts return_value
              

Local Variables

A local variable is a variable whose scope ends (goes out of context) when the function returns

      def doubleThis num
        numTimes2 = num*2
        puts num.to_s+' doubled is '+numTimes2.to_s
      end

      doubleThis 44
      puts numTimes2.to_s     
      

      44 doubled is 88
      # >
      
      

Let's Develop It!

Let's write a method takes in a String question and returns an answer.

            def method_name(parameter)
              # method implementation
            end
            

Keeping Track of Program Flow

Splat Arguments

Only in 1.9 or newer

The Splat or asterisk operator will capture however many arguments you pass into greet.

            def greet(greeting, *names)
              names.each do |name|
                puts "#{greeting}, #{name}!"
              end
            end

            >> greet("Hello", "Alice", "Bob", "Charlie")
            Hello, Alice!
            Hello, Bob!
            Hello, Charlie!
              

For more explaination check out this link

Default Values

If using 1.9 or lower, these have to be the last arguments in your list.

Default values are used if the caller doesn't pass them explicitly.

            def eat(food = "chicken")
              puts "Yum, #{food}!"
            end

            >> eat
            Yum, chicken!

            >> eat "arugula"
            Yum, arugula!
              

Hashes as Parameter

            def add_to_x_and_y(amount, vals)
              x = vals[:x]
              y = vals[:y]
              x + y + amount
            end

            add_to_x_and_y(2, {:x => 1, :y => 2})
              

Named Parameters

To pass variable parameters, or to pass named parameters,
you can use an options hash.

            def bake(name, options = {})
              flour = options[:flour] || "rye" #this is like setting a default value
              creamer = options[:creamer] || "cream"
              puts "baking a nice #{flour} loaf with #{creamer}"
            end

            bake("Wheat")
            bake("Sourdough", :flour => "sour")
            bake("Pumpernickel", :creamer => "butter")
              

Let's Develop It!

Lets write a method called englishNumber. It will take a number, like 22, and return the english version of it (in this case, the string 'twenty-two'). For now, let's have it only work on integers from 0 to 100.

Objects

An Object is an instance of a Class

Objects do things and have properties.

Object: Number

Object Class

Objects can be grouped by Class.

Classes define a template for objects. They describe what a certain type of object can do and what properties they have in common.

There are many kinds of objects, including
String, Number, Array, Hash, Time, ...

            array = Array.new
            

Object Methods

Methods can be defined on objects.

            array = Object.new

            def array.delete
              puts "deleted the array"
            end

            array.methods(false)
                    

Instance Variables

Represent object state

Represent object state

Names start with an @

Only visible inside the object

            cookie = Object.new

            def cookie.add_chips(num_chips)
              @chips = num_chips
            end

            def cookie.yummy?
              @chips > 100
            end

            cookie.add_chips(500)
            cookie.yummy?   #=> true
                    

Object Oriented Programming

• Object Oriented Programming is one of many programming approaches: procedural, event-driven, functional, declarative...
• These days, most programming is done in an OO language: Java, C#, C++.
• All this means is that programs are organized around objects (data & methods).
• You might choose OOP because Objects make things easier to understand and act as a natural way to modularize code. When a large code base is composed of many small Objects, it is easier to maintain and change.

OOP & Easy Understanding

Objects often take on names from their domain which makes them easy to conceptualize.

For example, without seeing my code, you can probably guess what an object called Bike can do (or not do)

OOP & Encapsulation

One thing that makes code easier to maintain is Encapsulation which is one of the fundamentals of OOP.

Encapsulation is a nice way of saying "put all my properties/behaviors in my capsule where other objects can't touch them".

By assigning certain responsibilities to objects, code is more purposeful and less likely to be changed by accident.

OOP & Inheritance

Just as you inherited traits from your mom, your objects may inherit traits from other objects.

Inheritance is when you use one class as the basis for another.

                          class MyString < String
                          end

                          my_string = MyString.new
                          my_string.upcase
                        

OOP & Polymorphism

• Similar to inherited traits and behaviors, there are also polymorphic traits and behaviors.
• Polymorphic means many forms.

                [1, "abc"].each {|object| puts object.next}
              

Questions?

Homework

Use the ask method to enhance your text-based Adventure game.

How many other methods can you make for actions in your game? Be prepared to share!

Homework

Expand upon englishNumber. First, put in thousands. So it should return 'one thousand' instead of 'ten hundred' and 'ten thousand' instead of 'one hundred hundred'.

Expand upon englishNumber some more. Now put in millions, so you get 'one million' instead of 'one thousand thousand'.

Then try adding billions and trillions. How high can you go?

How about weddingNumber? It should work almost the same as englishNumber, except that it should insert the word "and" all over the place, returning things like 'nineteen hundred and seventy and two', or however wedding invitations are supposed to look. I'd give you more examples, but I don't fully understand it myself. You might need to contact a wedding coordinator to help you.

Setup   |   Class 1   |   Class 2   |   Class 3   |   Class 4