#!/usr/bin/perl
use strict;
use warnings;
# Non-recursive method for generating Fibonacci series
#
# This is based on one liner found here:
# http://3monkeyweb.com/3monkeys/2007/07/12/fibonacci-series-in-one-line-of-perl/
#
# Amendments and comments made by Victor Odlivak 8/2/7
#
# usage:  ./perl_no_recur_fib  i
#
# where i is an integer between 0 and 73.
#
# This is the one liner:
#perl -e'@p=(0,1);until($#p>74){print"$p[-2]\n";push @p,$p[-2]+$p[-1]}'
#Here it is in a more intelligible form:
sub Fibonacci {
#
# input = number of iterations, followed by array.
# output = the last Fibonacci element for this iteration.
# i.e. Fib(5) = 5
#  Fib(0) = 0
# Fib(1) = 1;
# Fib(2) = 1;
# Fib(3) = 2;
my ($num_iterations, @p) = @_;     
until($#p>$num_iterations) # loop through array as it grows.
{
# Note, $#p is the last index value of the array "p";
# Note, the Fibonacci array starts with last index of 1
# for [0, 1] and progresses by one every time we go 
# through the loop. We are using the fact that the push
# had the side effect of incrementing the the count of the
# last index. 
#print "this is dollar_pound_p; $#p \n";
push @p,$p[-2]+$p[-1]; # add two elements of array and push at end.
}
return "$p[-2]"; 
}

#Main Section
my  $number_of_iterations = shift@ARGV;
my $result = 0;
my @q = (0,1); #starting Fibonacci array. Note, you can
# start later in the sequence if you like, i.e. (5,8)
unless ($number_of_iterations) {
   print "Sorry, you forgot to enter the number of iterations ";
   print "for the Fibonacci series. i.e.: ./perl_no_recur_fib 10 \n";
   exit;
}
if (($number_of_iterations > 73) or ($number_of_iterations < 0)) { 
   print "iterations must be between 0 and ";
   print " 73 for accurate values.\n";
   exit;
   }
$result = Fibonacci($number_of_iterations, @q);
print "Fibonacci($number_of_iterations) element of the series = ";
print "$result \n";
exit;