Calculate E in Ruby

e.rb

#!/usr/bin/env ruby
# Watch how E changes as n increases
# For good display, I set the cursor off
# To make your cursor appear again, try ``printf "\033[?25h"

def e(rounds)
  print "\033[?25l"
  for n in 1..rounds do
    e = (1 + 1.0 / n) ** n
    if n % 10 == 0
      print "On round #{n}, E = #{e} \r"
    end
  end
  puts "On round #{n}, E = #{e}"
  print "\033[?25h"
end

if ARGV.empty?
  print "Calculate to what round? : "
  rounds = gets.to_i
else
  rounds = ARGV[0].to_i
end

e(rounds)