nawn.rb

puts "Gimme numbars! Say 'done' as appropriate."

nums = ARGF.take_while { |line| line.chomp.upcase != 'DONE' }
           .map { |n| n.delete(?,).to_i }

puts "These are teh numbars: #{nums}"

puts "Which op you wantses? add(+1), sub(-2), mul(*3), div(/4)"

valid = %w[add sub mul div 1 2 3 4 + - * /]
op = gets.chomp until valid.include? op
op = '+-*/'[valid.index(op) % 4]

puts "#{nums * op.center(3)} = #{nums.reduce op}"