#! /usr/bin/ruby
# show results of compound interest

begin
  p = ENV['p'].to_f
  r = ENV['r'].to_f
  y = ENV['y'].to_f
  r /= 100
  p2 = p * ((1 + r) ** y)
  puts "ending principal: #{p2}\tgain: #{p2 - p}"
rescue
  STDERR.puts "usage: p=1000 r=4.85 y=5 compound"
end