calculate_ira.rb

def balance_to_dollars(balance)
  balance = "#{'%.2f' % balance}"
  dollars = balance.split('.')[0]
  cents   = balance.split('.')[1]
  dollars = dollars.reverse.gsub(/...(?=.)/,'\&,').reverse
  "$#{dollars}.#{cents}"
end

print "What is your current age? "

start_age = gets.chomp.to_i

print "What age would you like to calculate through? "
goal_age = gets.chomp.to_i

print "What is the current balance of the account? "
current_balance = gets.chomp.to_i

print "How much are you going to deposit each year? "
yearly_deposit = gets.chomp.to_i

print "What yield percentage would you like to calculate at? "
yield_percentage = gets.chomp.to_i / 100.0

(goal_age - start_age + 1).times do |i|
  current_age = start_age + i

  if i == 0
    puts "You started at age #{start_age} with #{balance_to_dollars(current_balance)}."
  else
    current_balance += yearly_deposit
    current_balance *= (1 + yield_percentage)

    puts "At age #{current_age} you will have #{balance_to_dollars(current_balance)}."
  end
end