Programming

Operating System (OS)

Talk to a computer's hardware.

Application

The software. It sends input (commands, data, etc) to the operating system and receive output after the operating system has acted on it.

Language

A set of code that can be used to create an application.

• Ruby
• Python
• Perl
• Java
• C++

Many others.

Q: How is a computer language similar to a human language, like English or Spanish? How is it different?

Library

A collection of reusable code to accomplish a generic activity.

Framework

Collection of reusable code to facilitate development of a particular product or solution.

Ruby vs. Rails

Ruby is a language

Gems are Ruby libraries

Rails is a framework

Ruby vs. Rails

• Rails is written in Ruby language.
• Rails contains many Ruby gems.
• Rails is a framework.
• Rails' purpose is to build websites.

The rest of this tutorial isn't about Rails. You're learning how to do any kind of programming with Ruby.

Prompt

• Terminals show a line of text when you login & after a command finishes
• It's called the prompt, and customarily ends with a dollar sign

Whenever instructions start with "$ ", type the rest of the line into terminal.

Let's give the terminal a command, to open Interactive Ruby (IRB)

  $ irb

Variables

A variable holds information.

• We give it a name so we can refer to it
• The info it holds can be changed

  $ irb
  > my_variable = 5
  => 5
  > another_variable = "hi"
  => "hi"
  > my_variable = 10
  => 10

What is happening on the lines beginning with => ?

• Setting a variable equal to something is called "assignment." In the above examples, we are assigning my_variable to 5 and my_other_variable to "hi."
• What types of information can we hold in a variable? (see next slide for answers)

Variable

Variable Assignment

Variables are assigned using a single equals sign (=).

The right side of the equals sign is evaluated first, then the value is assigned to the variable named on the left side of the equals.

  apples = 5
  bananas = 10 + 5
  fruits = 2 + apples + bananas
  bananas = fruits - apples

What happened on each line? Is it what you expected?

What could you do to see each's return value for confirmation?

Numbers

• Numbers without decimal points are called integers and numbers with decimal points are called floats.
• Examples of integers:
  • 0
  • -105
  • 898989898
  • 2
• Examples of floats:
  
  • 0.0
  • -105.56
  • 0.33
  • 0.00004
• You can perform operations on both types of numbers with these characters: +, -, /, *

exercises

• Try dividing an integer by an integer. Try dividing an integer by a float. How are the results different?
• Create two integer variables called num1 and num2 and assign them your favorite numbers.
• Next, compute the sum, difference, quotient, and product of these two numbers and assign these values to variables called sum, difference, quotient, and product, respectively.

Collection

Collection types: Array, Hash

• In the following slides, we will cover the following topics:
  • Definition of an Array
  • Array syntax
  • Array indexing
  • Array methods
  • Definition of a hash
  • Hash syntax
  • Hash indexing

Collection

Array

An array is a list.

Each array must be surrounded by square braces aka square brackets. A comma separates each member.

> fruits = ["kiwi", "strawberry", "plum"]
=> ["kiwi", "strawberry", "plum"]

exercises

• Make your own array and name it grocery_list.
• Include at least 5 items from your grocery list in the array.

Collection

Array

Indexing

Members are stored in order. Each can be accessed by its index. Ruby starts counting at zero.

> fruits[0]
=> "kiwi"
> fruits[1]
=> "strawberry"
> fruits[2]
=> "plum"

exercises

• Still have your grocery_list array? Good, because we're going to use it in this exercise.
• What is at index zero in your grocery_list array? How about index 5? Guess the answers and then use the syntax in the examples above (eg: fruits[0]) to see if your guesses were right.

Collection

Hash

In a hash we can refer to a member by a keyword instead of a number. Each member is a pair:

• Key: address of the hash member

• Value: variable contained by the member, and located by key name

A hash may also be known as a dictionary, associative array, or map.

Collection

Hash

Hash Syntax

A hash is surrounded by curly braces aka curly brackets. A comma separates each member pair. A key uses => (the rocket) to point to its value.

> states = {"CA" => "California",
"DE" => "Delaware"}
=> {"CA"=>"California", "DE"=>"Delaware"}

In real life, what lists do we make in key/value pairs?

exercises

• Define a Hash variable called my_info which has the following keys:
  • "first_name"
  • "last_name"
  • "hometown"
  • "favorite_food"

Collection

Hash

Hash Indexing

Member pairs can be accessed by their key. So each hash key has to be unique.

Values don't have to be unique.

> states["CA"]
=> "California"

exercises

• Add the key "good_food" to your my_info hash and give it the same value as your favorite_food key. What happens?
• Add a second "favorite_food" key to your my_info hash. What happens when you print out the has hash again? Why?

Methods

things that do stuff.

• "If objects (like strings, integers, and floats) are the nouns in the Ruby language, then methods are like the verbs." - Chris Pine's "Learn to Program"
• Methods are called (used) with a "."
  
  • Example: 5.to_s (to_s is the method)
• As it turns out, 5 + 5 is really just a shortcut way of writing 5.+ 5.
• Each data type (string, integer, float) has a set of built in methods. You can see all of the string methods here: http://ruby-doc.org/core-1.9.3/String.html (there are tons - don't worry about memorizing them, just good to know where you can go to find out more)

exercises

• Create a String variable called old_string and assign it the value "Ruby is cool"
• Use String methods to modify the old_string variable so that it is now "LOOC SI YBUR" and assign this to another variable called new_string.
  • Hint: look at the string methods "upcase" and "reverse"

Boolean

A boolean is one of only two possible values: true or false.

  > 1 + 1 == 2
  => true
  > 1 + 1 == 0
  => false

( == means "is equal to". More on that later.)

exercises

• Create a variable named favorite_color and assign it to your favorite color.
• Create a variable named not_favorite_color and assign it to a different color.
• Test to see if these variables are equal.

Operators

Do stuff with objects

  > my_variable + 2
  => 7
  > my_variable * 3
  => 15

  > my_fruits = fruits + ["lychee"]
  => ["kiwi", "strawberry", "plum", "lychee"]
  > my_fruits = my_fruits - ["plum"]
  => ["kiwi", "strawberry", "lychee"]

exercises

• Create an array called "vegetables" than contains 3 vegetables you like and 1 vegetable you don't like.
• Using the vegetables array, create an array called "my_vegetables" that contains only the vegetables you like.
• Extra: can you use the first two arrays to create a third array called "your_vegetables" that only contains the vegetable you don't like?

Loop

Does something repeatedly

  > fruits.each do |fruit|
  ?> puts fruit
  > end
  kiwi
  strawberry
  plum
  => ["kiwi", "strawberry", "plum"]

On the second line, what does ?> indicate?

exercises

• Create an array of 4 places you would like to visit.
• Print out each of these places using a loop.
  • Example:

"I would like to visit Barcelona"
"I would like to visit Antigua"
"I would like to visit Alaska"
"I would like to visit New Orleans"

Conditional

Do something only if a condition is true

  > fruits.each do |fruit|
  ?> puts fruit if fruit == "plum"
  > end
  plum
  => ["kiwi", "strawberry", "plum"]

exercises

• Create an array called "group" that contains the names of some of the people in your Railsbridge group. Make sure you include your own name.
• Using your group array, create a conditional that prints "My Name is (your name)" for your name only.

Running Your Code

Running code from a file

Create the file

• Why use a file? What's different from, say, irb?

Note which folder your terminal is currently in, this is your working directory

In your text editor, create a file named my_program.rb inside your working directory.

class Sample
  def hello
    puts "Hello World!"
  end
end

s = Sample.new
s.hello

Object Oriented Programming (OOP)

Class

Describes the generic characteristics of a single type of object.

What things of this type are.

e.g. Dog, Vehicle, Baby

Method

Defines behavioral characteristic.

What the things of the class's type do.

e.g. Chase, Drive, Talk

Variable

Defines attribute characteristic.

What things of the class's type have.

e.g. Breed, Model Year, Favorite Ice Cream

Instance

A specific incarnation of the class.

e.g. Rin Tin Tin, garbage truck, the neighbor's kid

Let's Create Projects!

Project 1:

Personal Chef Lab

(start at "4. Objects, Attributes, and Methods")

Topics:

• Commandline program. Practice in Ruby syntax and OOP concepts, and creating commandline programs.

• Explore strings: concatenation, manipulation, interpolation, coercion.

• Symbols, nil, basic math operators, blocks, method chaining, passing parameters to methods, iteration, branching, conditionals & conditional looping.

Project 2:

Encryptor Lab

Topics:

• Commandline program. Reinforce skills learned in Personal Chef.

• Explore how to manipulate arrays, do more elaborate strings manipulations, refactor code, take advantage of character mapping, and access the filesystem from within code.

Project 3:

Event Manager Lab

Topics:

• Commandline program. Reusing others code & data, refactoring your own code & cleaning up data, writing custom code to solve requirements.

• Gems, initialize method, parameters, file input/output, processing/sanitizing data, looping, conditional branching, using file-based data storage (CSV, XML, JSON), accessing an external API, nils, DRY principle, constants, sort_by, more string manipulations.

Project 4:

Testing & More

A follow-up to EventManager focusing more on Ruby object decomposition and working with Command Line Interfaces and program control flow.

1. Testing Topics: TDD, BDD, Rspec (stop at "Exceptions")

2. Event Reporter Lab Topics: Object decomposition, working with Command Line Interfaces, and program control flow. Continues project created in Event Manager lab.

3. Rspec