From: Sharon Phillips <phillipsds@...>
Date: 2007-11-30T20:53:06+09:00
Subject: Re: Trouble with a while loop

Hi Bashka,

I've had a it of a shot at your code, mainly looking at reducing the  
repetition and catching a few of the cases that might cause an endless  
loop (like if no-one bid higher than the valuation.

It looks from your code like you newish to programming, so there's a  
fair chance I've used some constructs not familiar to you. If so, let  
us know and someone will help explain. This is only a quick attempt  
(I'm supposed to be unpacking boxes - we've just moved house) and a  
bit messy.

Here tis:

class Bidder
   attr_reader :still_bidding, :num

   def initialize num, reserve_price, max_bid
     @num= num
     @max_bid= max_bid
     @margin= @max_bid- reserve_price
     @bid= reserve_price+ @margin/2
     @still_bidding= @max_bid> reserve_price
   end

   def current_bid
     @bid
   end

   def raise_bid
     @bid+= @margin/4
     @still_bidding= @bid<= @max_bid
   end
end

@bidders= []

def get_num msg
   print "#{msg} >"
   gets.to_i
end

#we're only interested in bidders who haven't yet reached their max
def bidders_left
   @bidders.select {|bidder| bidder.still_bidding}
end

valuation= get_num "Enter the valuation"
reserve_price= get_num "Enter the reserve price"

#set up the bidders
(1..(get_num "How many bidders?")).each do |index|
   max_bid= get_num "How much is invester #{index} willing to spend?"
   @bidders << Bidder.new(index, reserve_price, max_bid)
end

#no-one's won yet, and we haven't started
winner= nil
round= 0

while bidders_left.any? && winner.nil?
   print "\nRound #{round+=1}: "

   #get the current lowest bidder
   current_bidder= bidders_left.sort{|a,b| a.current_bid <=>  
b.current_bid}.first

   bid= current_bidder.current_bid
   puts "Investor #{current_bidder.num} is bidding $#{bid}"

   #either they won, or they raise their bid
   if bid> valuation
     winner= current_bidder
   else
     current_bidder.raise_bid
   end
end

if winner.nil?
   puts "No one bid high enough. Property passed in"
else
   puts "** This property has been sold to Invester  
#{current_bidder.num} **"
end


On 30/11/2007, at 8:00 PM, Bashka Dooble wrote:

> Hi,
>
> Please forgive if this forum is not the right one for this post.
>
> I'm writing a small ruby program that implements sale of a plot of  
> land
> to 5 investors through English Auction. In an English auction, the
> auctioneer begins the auction with the reserve price (lowest  
> acceptable
> price) and then takes larger and larger bids from the customers  
> until no
> one will increase the bid. The item is then sold to the highest  
> bidder.
>
> The logic that i'm using to decide which investor to bid first is  
> this:
> 1. Each investor has a maximum willing price that they can't exceed.
> 2. First find out the difference/margin btw an investor's willing  
> price
> and the reserve price
> 3. The investor that has the lowest margin bids first
> 4. An investor's first bid = reserve price + half of margin
> 5. Subsequent bids = first bid + 25% of margin i.e. half of the other
> half of margin
>
> The code as it is now is attached.
>
> Thanks,
>
> Bashka
>
> Attachments:
> http://www.ruby-forum.com/attachment/1072/engBid42.rb
>
> -- 
> Posted via http://www.ruby-forum.com/.
>