Intro to Ruby

Class 1

Welcome!

Girl Develop It is here to provide affordable and accessible programs to learn software through mentorship and hands-on instruction.

Some "rules"

  • We are here for you!
  • Every question is important.
  • Help each other.
  • Have fun!

Homework Discussion

How was last week's homework? Do you have any questions or concepts that you'd like to discuss?

What we will cover today

  • What is programming?
  • Why Ruby?
  • Variables, Arithmetic & Objects
  • Methods and Error Messages

What is programming?

  • Teaching the computer to do a task.
  • A program is made of one or more files of code, each of which solve part of the overall task.
  • Programming code is human readable but also needs a form that the computer can run directly. This form is not human readable.

Why Ruby?

  • It reads like English. The syntax is intuitive.
    •               
# Java
for(int i = 0; i < 5; i++)

# Ruby
5.times do
  • The community is large, active and interested in helping others learn.
  • You can get a web app off the ground quickly.
  • You can make a lucrative career out of it.
  • Using Ruby will cost you $0.

What is Ruby used for?

  • Web development (Rails)
  • iPhone apps (RubyMotion)
  • System Administration (Chef)
  • Testing (Vagrant)
  • Security (Metasploit)

Who is using Ruby?

Working with IRB

  • IRB is a command line interface to ruby that is installed when we install Ruby. It works like a calculator and is a great way to get started quickly.
  • Open: type `irb`
  • Quit: Type `quit` and then press `enter`
  • Follow along with the examples in the slides. Type them in!
  • Feel free to explore as well. You will not accidentally break things.

Arithmetic

Try out some calculator functions

            
3 + 4
2 * 4
6 - 2
4 / 2
4 /* 2
=> SyntaxError: (irb):10:syntax error, unexpected *

Errors are Neat!

  • There are different kinds of errors that can occur. We just saw the SyntaxError which often helps us find misspelled words or missing quotes.
  • Take time to read each Error. They often tell you how to fix the issue and can be a great starting point when searching for help online. 
            
irb> hi
NameError: undefined local variable or method `hi' for main:Object

Variables

  • Variables are references to information.
  • We reference variables by name.
  • They are called variable because the information they reference may change.

# Everything after this pound sign will not be evaluated.
# These are called comments and I will use them to annotate code
age = 50
days_in_year = 365
days_alive = age * days_in_year
=> 18250

Ruby's Variables

  • Ruby has three kinds of variables, one kind of constant and exactly two pseudo-variables.
  • A local variable starts with a lower case letter or an underscore character (_) and consists entirely of letters, numbers and underscores.

age = 50
_age = 50
_my_age = 50

What can I do with a Variable?

  • Create - Initialize
  • Access - Read
  • Assign - Replace

# create and assign in one line
age = 0

# access the value in age
age

# replace value in age
age = 40

Variable naming

  • Express what is stored inside
  • Make it easy to read
  • Should be understood by someone who has no idea what your program does
  • Should be unique

# good
occupation = "software engineer"

# bad
occupation_i_always_dreamed_of_having_in_seattle = "software engineer"
o = "software engineer"
1st_occupation = "software engineer"

Local Variable Values

  • No default value
  • No type declaration
  • Do not live forever

# error
name

name = "Heather"
defined?(name)

Data Types

Built-in: Numbers, Strings, Symbols, Booleans, Regular Expressions, Arrays, Ranges & Hashes

  • Data always has a "type"
  • You will hear the words Class/Type/Object used interchangeably
  • Let's explore a few built in Objects

irb> 1.class
=> Fixnum
irb> "Hello".class
=> String
irb> 1.0022.class
=> Float
irb> [1,2,3].class
=> Array

Strings

Strings are characters inside double or single quotes.


a = 'Hello '
b = "World"
c = a + b
c.reverse
=> "dlroW olleH"
          

a = "Spam "
b = a * 4
# Here multiplying a "Spam " by 4 concatenates (links) four strings
=>"Spam Spam Spam Spam "
together

String Practice


"Heather".upcase
"Heather".downcase
"heather".capitalize
"Hello".reverse
"Heather".length
"Heather Moore".swapcase
"".empty?

What is the reverse of your name?

How many characters long is your name?

Can you repeat the word hello 100 times?

What is the 5th character of my name?

Numbers

Numeric data comes in two types: Integers and Floats

Integers are either Fixnum or Bignum. They do not have decimals.


irb> 1_000_000_000_000_000_000.class
 => Fixnum
irb> 1_000_000_000_000_000_000_000.class
 => Bignum

Floats are numbers with at least one number to the left of a decimal point.


            irb> 1.001.class
             => Float

Number Practice


7/8
7.0/8.0
3.14.to_s
3.14.to_i
1 + "2"
1 + "2".to_i
(1 + 2) * 3
1 + (2 * 3)

How many seconds are in an hour?

How many minutes are in a week?

How many years old are you if you've been alive 1 million seconds?

Symbols

You can think of symbols as lightweight Strings.

It's good to know these exist, but don't think about them too much for now.


# transient and mutable
"hello"

# permanent and immutable
:hello

Booleans

This is another Object that we will learn about later.

For now, when you hear Boolean, think TRUE and FALSE.


# NOT true
!true
=> false

# NOT false
!false
=> true

Arrays, Ranges & Hashes

We will also leave these data types for the next class

Examples of what they will look like:


# Arrays are used to hold sets of data.
irb> array_of_numbers = [1,2,3]
irb> array_of_numbers.first
=> 1

# Ranges are used to express a sequence.
irb> range_of_numbers = (1..5)
irb> range_of_numbers.include?(4)
=> true

# Hashes are like dictionaries. You can look up a value by a key.
irb> hash_of_key_to_value =
  {
    "Apple" => "A fruit.",
    "Cucumber" => "A vegetable."
  }

Methods

  • Methods define the behavior for an Object.
  • String Objects can reverse, for example.
  • Some methods are accessed using our friend 'dot' and some are standalone.
  • Let's call some methods
            
irb> puts "hello"
hello
=> nil
irb> "2".to_i
=> 2
irb> 2.to_s
=> "2"
irb> "2" / 5
NoMethodError: undefined method `/' for "2":String

User Input

  • To obtain user input, use `gets`
  • To print out information, use `puts`
  • Let's create our first program together


Put the code below in a file and save it as name.rb


puts 'Hello there, and what\'s your name?'
name = gets
puts 'Your name is ' + name.chomp! + '? What a lovely name!'
puts 'Pleased to meet you, ' + name + '. :)'

Run your program from the command line:


        ruby name.rb

Let's Develop It

  • Write your own program using 'puts' and 'gets' to ask a user for their age and then tell them how old they are in dog years.
  • reminder: 'gets' method returns a string. To do math on it, convert it to an integer with .to_i method.
    • 
            #1 dog year = 7 human years
            user_age = gets.to_i

Lab 1

  • Update your code to return a message in all capital letters.

# YOU ARE 5 YEARS OLD IN DOG YEARS

Lab 2

  • Update your code to return a message in all capital letters, reversed with a count of the characters returned in parens.

# YOU ARE 5 YEARS OLD IN DOG YEARS (32 characters)

Questions?

Homework

Practice: Write a command line program that asks the user for their birthday (be sure to specify format), then calculates their age in years, days, and seconds. Tell the user how old they are in these different formats. (Note: you'll be using 'gets' and 'puts' in this program, along with some math!)

Prep: Read Chapter 6 and Chapter 7 of Learn To Program- don't try to do the exercises at the end yet, though.