24.rb

puts "Welcome to uber-calculator"
puts "Please enter commands in the format:"
puts "\tX op Y"
puts "Prefix 0x for hex, 0b for binary"
puts "... hell, lets do octal too!"
puts "Type q(uit) to, y'know, QUIT!"
puts "Output in base 10, change output base with base = N"

class String
  def to_10
    base = nil
    if self =~ /^0b([01]+)/
      return $1.to_i(2)
    elsif self =~ /^0x([\dabcdefABCDEF]+)/
      return $1.to_i(16)
    elsif self =~ /^0([01234567]+)/
      return $1.to_i(8)
    elseif self =~ /[\d]+/
      return to_i
    else
      raise "Frak!"
    end
  end
end

while(print ">>"; input = gets and input !~ /q(uit)?/i)
  tokens = input.split(/\s+/)
  if tokens.size != 3
    puts "uh uh uh, didn't say the magic word!"
    next
  end
  
  first, op, second = tokens
     
  if first=="base" and op=="="
    begin
      $base = second.to_10
      raise "That's WAYY too big (that's what she said)" if $base > 36
    rescue
      $base = 10
    end
    puts "Base set to #{$base}"
    next
  end  

  unless %w|+ - * /|.include? op
    puts "I don't even know what the hell you are trying to do, try one of these: + - * /"
    next
  end

  begin
    answer = first.to_10.send(op.to_sym, second.to_10)
    puts "#=> #{answer.to_s($base)}"
  rescue
    puts "So, there was an error, and we lost both your numbers"
  end
end
puts "OK, LOVE YOU BYE!"