Are YOU ready for Waterloo CS?

[Martin]

http://www.cs.uwaterloo.ca/undergrad/admissions/placement/cs134.shtml

This is the test to see if you are ready for CS 134 (the most advanced of the three first year choices for computer science) at the University of Waterloo.

Note: don't email it to the guys unless you actually are attending the university .

[Dan]

dose not seem that hard to me, i think i had a question alot like that on my grade 12 compsci exame that was on java.

[wtd]

It does seem pretty easy.

[Dan]

Well i guse they do not expceted you to know everything, alot of poleop could have had no compsci corses during high school and/or not progaming excpicen at all. So that whould probly be a good way to weed out any one that has no progaming excpricne from going in to the highested 1st year level right away.

[wtd]

And, I suppose, to figure out which people are willing to take the time to figure it out, if they didn't already know.

Would it be wrong to post a solution in another language?

I keep hacking stuff together to work my mind around the baroqe syntax of O'Caml.

[Martin]

Post it if you want. It's not a test or anything, and anyone at this point who's in CS 134 is stuck in CS 134. Also, Dan, it's required that you have ICS 3M to get into this course (and a teacher recommendation...a joke to get).

[wtd]

The module:

code:

module RealEstate =         struct                 let sum_list = List.fold_left (fun a b -> a +. b) 0.                         class agent name =                         object(self)                                 val mutable commissions = []                                                                 method get_name = name                                 method name_nil = name = ""                                                                 method add_commission amount =                                          commissions <- amount :: commissions                                                                         method total_commissions = sum_list commissions                         end                                         exception No_listing_agent                                         class basic_property address init_asking_price =                         object(self)                                 val mutable asking_price = init_asking_price                                 val mutable selling_price = 0                                 val mutable listing_agent = ref (new agent "")                                 val mutable selling_agent = ref (new agent "")                                 val mutable sold = false                                                                 method private listing_agent_commision_rate = 0.                                 method private selling_agent_commision_rate = 0.                                                                 method get_asking_price = asking_price                                 method get_selling_price = selling_price                                                                 method get_address = address                                                                 method increase_asking_price_by amount =                                         asking_price <- asking_price + amount                                                                         method decrease_asking_price_by amount =                                         asking_price <- asking_price - amount                                                                         method set_selling_price amount =                                         selling_price <- amount                                                                         method has_listing_agent = not !listing_agent#name_nil                                 method has_selling_agent = not !selling_agent#name_nil                                                                 method get_listing_agent = !listing_agent                                 method get_selling_agent = !selling_agent                                                                 method set_listing_agent new_agent =                                         listing_agent <- ref new_agent                                                                 method set_selling_agent new_agent =                                         selling_agent <- ref new_agent                                                                         method sold = sold                                 method set_sold = sold <- true                                                                 method as_string =                                         if sold then                                                 Printf.sprintf "The property at %s sold for $%d" address selling_price                                         else                                                 Printf.sprintf "The property at %s is for sal, asking $%d" address asking_price                                                                         method close =                                         let listing_agent_commission =                                                 ((float_of_int selling_price) *. self#listing_agent_commision_rate) and                                         selling_agent_commission =                                                 ((float_of_int selling_price) *. self#selling_agent_commision_rate) in                                                 if self#has_listing_agent && self#has_selling_agent then                                                         begin                                                                 !listing_agent#add_commission listing_agent_commission;                                                                 !selling_agent#add_commission selling_agent_commission                                                         end                                                 else if self#has_listing_agent then                                                         let total_commission = listing_agent_commission +. selling_agent_commission in                                                                 !listing_agent#add_commission total_commission                                                 else                                                         raise No_listing_agent;                                                 self#set_sold                         end                                         class residential_property address init_asking_price =                         object(self)                                 inherit basic_property address init_asking_price as super                                                                 method private listing_agent_commision_rate = 0.02                                 method private selling_agent_commision_rate = 0.03                         end                                         class rental_property address init_asking_price rental_income =                         object(self)                                 inherit basic_property address init_asking_price as super                                                                 method private listing_agent_commision_rate = 0.03                                 method private selling_agent_commision_rate = 0.03                                                                 method rental_income = rental_income                                 method as_string =                                         super#as_string ^ Printf.sprintf ", and offers annual rental income of $%d" rental_income                         end         end

A simple sample:

code:

open RealEstate open Printf include RealEstate let prop = new residential_property "42 Oak St." 2_000 let lister = new agent "Bob Smith" prop#set_listing_agent (ref lister) prop#set_selling_price 3_000 prop#close Printf.printf "Commission: %f\n" lister#total_commissions

O'Caml: Because static typing can be useful, but explicitly stating those types is lame.

[Martin]

How do I do java inheritance without protected variables?

[wtd]

Darkness wrote:

How do I do java inheritance without protected variables?

Properly.

For something this simple, the child class shouldn't need to directly access the parent class' instance variables. Rather you use the interface exposed by the parent class.

This is where accessors (get, set) come in handy.

[Martin]

The inheritence that I was using was CRentalProperty extends CProperty.

Now, everything is the same as CProperty, except there is also an annual income.

How do I do this (efficiently) without using protected variables? And what's so bad about protected variables anyway?

[rizzix]

hmm nothing?!?

[wtd]

Darkness wrote:

The inheritence that I was using was CRentalProperty extends CProperty.

Now, everything is the same as CProperty, except there is also an annual income.

How do I do this (efficiently) without using protected variables? And what's so bad about protected variables anyway?

I'm guessing they want to see if you can realize that you don't need protected variables in this case.

Why would CRentalProperty need to access the instance variables of CProperty?

[wtd]

Feel free to peruse the attached file and comment freely.

Python version added.
Ruby version added.
Eiffel version added.

I love demonstrating the beauty of these languages.