t.rb

class Checkout
  def initialize
    @total = 0
  end

  PRICES = { "Apple" => 30, "Banana" => 50 }

  def scan(item)
    @total += PRICES[item]
  end

  def total
    @total
  end
end

checkout = Checkout.new
checkout.total # will print 0
checkout.scan("Apple")
checkout.total # will print 30

############################

def plus(count)
  string = ""
  count.times do |x|
    string += yield(x + 1)
  end
  string
end

puts plus(3) { "ding" }
puts plus(3) { |x| "...#{x}" }
puts plus(5) { |x| (x + 2).to_s }