From: vanjac12@... (Van Jacques)
Date: 2003-12-15T03:02:01+09:00
Subject: Re: prog for g.c.d. of 2 integers

"Robert Klemme" <bob.news@gmx.net> wrote in message news:<brcjq4$1ti1d$1@ID-52924.news.uni-berlin.de>...
> "Van Jacques" <vanjac12@yahoo.com> schrieb im Newsbeitrag
> news:70ae81fd.0312111642.26511e58@posting.google.com...
> 
> I really wouldn't call it "mod" since that makes users expect to calculate
> the equivalent of "a % b", which it doesn't.

Yes, mod is not a good name. I was going to change it to gcd but never did.

> > def mod(x,y)
> >   z = x % y
> >   if z == 0
> >     return y
> >   else
> >     w = mod(y,z)
> >   end
> > end
> >
> > puts "Enter the number of numbers for greatest common denominator."
> >
> > num = gets.chomp.to_i
> >
> > a = Array.new
> > b = Array.new
> > gcd = Array.new
> >
> > for i in 0...num
> >   a[i] = rand(999) + 1
> > end
> > puts a
> 
> You don't need to sort.

Yes. I don't know what I was thinking of.
 
> > b = a.sort.reverse
> > puts b
> > gcd[0] = mod(b[0],b[1])
> >
> > for i in 2...num
> > if (b[i] > gcd[i-2])
> >   gcd[i-1] = mod(b[i],gcd[i-2])
> > else
> >   gcd[i-1] = mod(gcd[i-2],b[i])
> > end
> > end
> > puts gcd[num-2]
> > ===========
> 
> Kind of a more complicated version of inject.  But why do you store the
> results in an array?  You just need one value:
> 
> gcd = a.shift
> a.each{|n|gcd=mod(gcd, n)}
> puts gcd
> 
> Kind regards
> 
>     robert

Again, good point. I should "finish" my programs better. I developed some bad
and sloppy habits since I wrote a lot of Fortran programs for research that I was
the only one to read. I used a lot of arrays, and here I use them when they aren't
required. 

The last 3 lines of your code
> gcd = a.shift
> a.each{|n|gcd=mod(gcd, n)}
> puts gcd

look like a good way to get the gcd of an arbitrary
number of numbers. (with mod(x,y) --> gcd1(x,y), say).

Van