Intro to Ruby

IRB
Open up the terminal and in bash type

ruby -v

Open up an Interactive Ruby Shell

irb

Play around with ruby

a = 1
b = a + 5
5 * 4 / 3

Rails has its own version of irb called rails console. We'll talk more about this in upcoming classes.
Try some more commands

print a
puts a

The difference between print and puts is that puts returns a new line character, print dos not. Both return nil.
Comments in ruby

# this is a comment

You may also run ruby scripts from ruby files. Create a file and open it up with your preferred editor.

subl test.rb

Add some ruby code to the file

# test.rb
a = 5
b = a - 2

To run this file from the command line, run ruby test.rb.

Get some user input

puts "What is your name?"
a = gets.chomp #use chomp to remove a new line character

puts "Your Name is #{a}"

and run the file from the command line.

ruby test.rb

Exercise 01
Write code to prompt users for their first name, then last name.

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

puts "What is your last name?"
last_name = gets.chomp
puts "Your name is #{first_name} #{last_name}"

Strings
Strings are defined using quotes. Let's make a string and check its class

my_string = 'this is a string.'
my.string.class

What is the difference between using single quotes (') and double quotes (")?

my_string = "My name is \" Drew \" "

name = "Drew"

puts "My name is #{name}"
puts 'My name is #{name}'

Some other string methods

"drew".capitalize
"drew".upcase
"drew".downcase
"drew".reverse
"drew".rindex("a")
name = "Drew"
name.upcase   # non-destructive
name.upcase!  # desctructive (this will change the actual variable

String Exercises
Rdocs: String
1.) Try to find a way to swap the case of letters in the docs.

"Hello".swapcase

2.) Try to replace a substring with another string

"Hello, friends".gsub('friends', 'world')

3.) Try to replace double characters with single, e.g. "Hello" => "Helo"

"This      is useful    for removing additional space   .".squeeze(" ")

Math Operations
Examples

5 * 5
2 + 2 + 1
10 / 2
10 / 3        # This returns 3. It rounds it down. If we want the decimal value, we need to define it as a float
10.0 / 3      # 3.33333
235234.class  # Fixnum < Integer
235234235234235234235234235234235234235234235234.class # Bignum < Integer
1232.0.class  # Float < Number
10 % 3        # Returns the remainder: 1
10 % 2        # Returns 0 (no remainder)
10 % 2 == 0   # Returns true

Write code that sets a variable b to the power of 2

b = 5
a = b ** 2

Write code that asks a user for two inputs and then return the multiplication result

# multiplication_result.rb
puts "Enter an input for multiplication"
a = gets.chomp
a.to_i!

puts "Enter another input"
b = gets.chomp
b.to_i!
puts "#{a} times #{b} equals: #{a * b}"

Objects
In Ruby, everythign is an object. Let's look at some examples.

true
true.class        # TrueClass < Object
a = "<y stringsa fassfsda"
a.object_id       # Gives an object ID
true.object_id    # This will return a single object ID (dependent on Ruby version); a singleton. There is only one true object. 
10 > 5            # true
5  < 2            # false
10 > 5.object_id  # false
5.object_id       # singleton id
true && true      # true
true && false     # false
true && (10 > 5)  # true
true || false     # true
false || false    # false
1 + 1 * 5         # 6
1 + (1 * 5)       # It's better to show the order of operations explicitly
(1 + 1) * 5       # 10
(10 > 4) || false # true
10 >= 10 || false # true
a = 5
a == 4            # false
a == 5            # true

Conditionals
Let's try using if .. elsif... else ... end

#testing_if.rb
puts "Give me a number"
number = gets.chomp.to_i

if number > 10
  puts "Your number is greater than 10"
elsif number > 5
  puts "Your number is greater than 5"
else
  puts "Your number is less than 6"
end

1.) Write code that asks users for the year of their car and then prints: future, new, old or very old.

puts "What is the year of your car?"

year = gets.chomp.to_i

if year > 2014
  puts "Future car"
elsif year > 2010
  puts "New car"
elsif year > 1995
  puts "Old car"
else
  puts "Very old car"
end

While
While will continue while a condition is true. This example will print 1 to 50 to the terminal. Note that x is incremented everytime it loops, thus giving a stopping point, and preventing it from looping infinitely.

x = 1
while x <= 50
  puts x
  x += 1
end

1.) Print numbers 5- to 1 using a while loop

x = 50
while x >= 1
  puts x
  x -= 1
end

2.) Print the first 30 odd numbers using an until loop.

x = 1
count = 0
until x > 59
  puts x
  x += 2
end

# alternative method 1
until x > 59
  puts x unless x % 2 == 0
  x += 1
end

# alternative method 2
until x > 59
  puts x if x.odd?
  x += 1
end

For loops
We usually use for loops when we know from what number to what number we want to loop. We may use while when we are waiting until a condition is met.

# for.rb
for i in 3..10
  puts i
end

1.) Write FizzBuzz in ruby: Write code that prints 1 to 100. If the number is divisible by 3, put Fizz, if it is divisible by 5, put Buzz, if it is divisible by 3 and 5, put FizzBuzz. Otherwise, put the number.

#fizzbuzz.rb

Type Checking

"Hello CodeCore".is_a? String
"hello CodeCore".is_a? Integer
10.is_a? Integer
"asdfasdf".is_a? Integer
nil
nil.class
a = nil
a.capitalize      # undefined method `capitalize` for nil:NilClass

Note: nil is different from undefined

a = nil
defined? b
defined? a        # local-variable

ogryzek/intro_to_ruby.md

Intro to Ruby