add shebang, fix loop, fix conversion, fix formatting

gistfile1.rb

#!/usr/bin/env ruby
# encoding: utf-8
bill = nil
loop do
  print "\rHow much you bill was (CZK): "
  bill = gets
  begin
          bill = Integer(bill)
          break
  rescue Object
  end
end

tipSize = rand(25)
tip = (bill/100.0*tipSize).round
total = bill+tip
length = total.to_s.length + 1

puts("Bill:   %#{length}i" % bill)
puts("%d%% tip: %#{length+1-tipSize.to_s.length}i" % [tipSize, tip])
puts("="*(8+length))
puts
puts("Total:  %#{length}i" % total)