array.rb

my_array = ["Ben", "Phelim", "Arthur"]
# indexes     0         1        2

my_array.length # return the number of element in the array

# CRUD

# Read

my_array[0] # first element of array
my_array.first
my_array[-1]
my_array.last

# Create

my_array.push("Lucien") # same as => my_array << "Lucien"

# Update

my_array[0] = "Alex" # Reassign the value at index 0

# Delete

my_array.pop # delete last element of the array
my_array.delete("Lucien") # delete all element having the value of "Lucien"
my_array.delete_at(-1) # Delete element at index -1

iterations.rb

my_array = ["Ben", "Phelim", "Arthur", "Alex"]

# Each - returns the original array
my_array.each do |name|
  puts name
end

# Each with index - returns the original array
my_array.each_with_index do |name, index|
  puts "#{index + 1} - #{name}"
end

# Map - returns a copy of the original array with element transformed
new_array = my_array.map do |name|
  name.upcase
end

# Count - returns an integer. counter is incremented if the condition is true
number = my_array.count do |name|
  name.start_with?("A")
end

# Select - returns an array with element matching the condition
starts_with_a = my_array.select do |name|
  name.start_with?("R")
end

# Reject - returns an array without element matching the condition
starts_with_a = my_array.reject do |name|
  name.start_with?("A")
end

timer.rb

# define a method timer
def timer
  start_time = Time.now
  yield # calls the block passed as an argument during the method call
  puts "Elapsed time: #{Time.now - start_time}s"
end

# method called with a block
timer do
  puts "starting task 1"
  sleep(2)
  puts "task 1 done!"
end

# method called with a block
timer do
  puts "starting task 1"
  sleep(1)
  puts "task 1 done!"
end

# def a method taking 2 parameters
def greet(first_name, last_name)
  full_name = "#{first_name.capitalize} #{last_name.upcase}"
  yield(full_name) # Calls the block passed as an argument during the method call
end

# method called with a block
greet('john', 'lennon') do |full_name|
  puts "Greetings #{full_name}, you look quite fine today!"
end

# method called with a block
greet('john', 'lennon') do |name|
  puts "Bonjour #{name}, comment ça va ?!"
end