Luhn algorithm

luhn.rb

def random(n)
  s = ''
  for i in 0..n-1
    s += rand(0..9).to_s
  end
  return s
end

def get_digit(s, i)
  output = 0
  if(i%2==0) # if we start from position 0, every even number will be multiplied by 2
    output = s[i].to_i*2
  else # if we start from position 0, every odd number will stay the same
    output = s[i].to_i
  end
  if(output > 9) 
    # if the outcome of the multiplication greater than 9
    # split the number and add them together
    output = output.to_s[0].to_i + output.to_s[1].to_i
  end
  return output
end

def get_checksum(s)
  a = Array.new
  for i in 0..s.length-1
    a.push(get_digit(s, i))
  end
  total = 0
  for i in 0..s.length-1
    # calculate the sum of all the numbers
    total += a[i]
  end
  # divide the total by 10 and gets the remainder
  remainder = total % 10
  output = 0
  if(remainder>0) # if the remainder is greater than 0 then take 10 and minus the remainder
    output = 10 - remainder
  end
  return output
end

def get_visa
  # fifteen = '%s%s' % [4, str_random(14)]
  fifteen = '499233836191683'
  return '%s%s' % [fifteen, get_checksum(fifteen)]
end

puts get_visa