      # Again, an EOF will except out of the pgm.
        while true
            # Request an integer.
            print "Enter x value or blank line: "
            x = readline.chomp
            break if x == ''
            raise EOFError.new if x == 'quit'

            # If it looks bad, let's try again.
            if x !~ /^\-?\d+$/
                print "That doesn't look like an integer.  Please try again.\n"
                next
            end

            # Convert to an integer and print the resul