Luhn checksum

luhn_checksum.rb

def check_sum val
  sum = val.to_s.each_char.with_index.inject([]) do |memo, (char, i)|
    next memo << double_digit_value(char.to_i) if i.odd?
    memo << char.to_i
    memo
  end.inject :+

  if (sum % 10).zero?
    p "#{sum} is divisible by 10. Valid!"
  else
    p "#{sum} is not divisible by 10. Invalid!"
  end
end
def double_digit_value digit
  double_digit = digit * 2
  sum = double_digit > 10 ? (1 + double_digit % 10) : double_digit
  return sum
end

puts 'Enter some number'
input_val = gets.chomp
begin
  check_sum input_val
rescue => e
  p e
end