MyNumberCheckDigit.rb

def get_check_digit (number)
    sum = 0
    number[0,11].reverse.split(//).each_with_index {|n, i|
        sum += n.to_i * (i % 6 + 2)
    }
    return sum <= 1 ? 0 : 11 - sum % 11
end

puts "Please input your number"
number = gets.chomp
if number.length != 12 then
    puts "Invalid number"
    exit
else
    if get_check_digit(number) == number[11].to_i then
        puts "Check Digit is valid"
    else
        puts "Check Digit is NOT valid"
    end
end