change.rb

class Currency
  def initialize(denominations) # denominatons of currency passed as hash
    @denominations = denominations
  end

  def make_change(amount)
    # determine change as minimim possible coinage
    @amount = (amount * 100).to_i # convert $ to ¢ //FIXME breaks abstraction
    @change = {}
    for key in @denominations.keys.sort.reverse    # keys MUST to be in desc order
      @change[@denominations[key]] = @amount / key # {coinage => quantity}
      @amount = Integer(@amount) % key             # amount = remaining amount
    end

    return @change.to_s
  end
end

def get_user_input
  puts "Enter an amount in dollars and cents [dollars].[cents]
        Please omit prepended $ or ¢ symbols
        Press only [enter] to quit"
  input = gets.chomp
  if(0 == input.length) # user hit only enter => exit
    puts "adios!"
    exit
  elsif(input =~ /^\d?(\.\d{2})?$/) # valid format $ || $.¢¢ || .¢¢
    return input
  else # invalid user input
    puts "invalid currency format"
    return nil
  end
end


while true
  amount = get_user_input.to_f
  if amount
    puts Currency.new({1=>"penny", 5=>"nickel", 10=>"dime", 25=>"quarter", 100=>"dollar"}).make_change(amount)
  end
end