ruby negative factorial and plus .

#!/usr/bin/env ruby
#ruby 2.0.0 version test
# negative factorial and plus each result number
n=ARGV[0].to_i
def n_fact(n)
  if n > -1
    puts "argument must be less then 0"
    elsif n == -1
     return n
    else
      return (n*n_fact(n+1))
   end
end

result = n_fact(n)
puts "negative fact value : #{result}"

def nf_sum(r)
    r = r.to_s
    if r[0] == "-"
       r1 = -(r[1].to_i)
       for i in 2..(r.size-1)
        puts "#{r1}+#{r[i]}=#{r1+=r[i].to_i}"
       end
        # putting result
        puts "So last sum is = #{r1}"
    else   # If the result value is positive
       sum = 0
       r.each_char { |r| sum += r.to_i }
       puts sum
    end
end


nf_sum(result)

#Testing ^^;
oyj@oyjmint ~/rp $ ruby negative_fact.rb -7
negative fact value : -5040
-5+0=-5
-5+4=-1
-1+0=-1
So last sum is = -1
oyj@oyjmint ~/rp $ ruby negative_fact.rb -8
negative fact value : 40320
9