Simple question (involving rand() i think)

Quote:

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Originally posted by AnthonyMai
[B]<B>It is an extremely bad idea to use Paul's random_shuffle() function to shuffle the deck as the OP requested.</B>

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On the contrary, I think it is an extremely good idea to use Paul's
random_shuffle() function. The original poster stated:
"I'm making a black jack program as an excersize [sic]...."

This is clearly not a complicated gamgling simulation; nor is it
going to be a security/crypography piece of software.

I don't understand why you'd bother to make this post, given the
fact that you stated:
"To sum up, I do not see how random_shuffle() in STL has any real usage, except for as some homework assignment for students."

This is exactly what the original poster is doing: doing an exercise
so that [s]he can learn about C/C++. My guess is that you're
still going about trying to make Paul McKenzie look bad.
Unfortunately, you've failed at this attempt too; better luck next
time.

--Paul

Quote:

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Originally posted by jfaust
Furthermore, random_shuffle can take a predicate argument, so you don't need to use rand().

Jeff

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Hello Jeff,

Anyone who is versed in standard C++ would have known this or would have taken just a few seconds to look it up. Here is the definition, for those who wish to criticize before they research:

http://www.sgi.com/tech/stl/random_shuffle.html

Note the second definition which takes a predicate.

Regards,

Paul McKenzie

One of the guarantees given in the standard for random_shuffle is that any given random sequence from N objects has a probability of appearing of exactly 1/N! - i.e there is no "clumpiness" to the result: it's evenly distributed over all possibilities.

BTW, I wouldn't use a vector<card>, I'd use a deque<card> :D .

Paul got his reply in as I was typing mine - look at the link under "Notes" for the behaviour guarantee.

Graham,

Do you recommend deque because you simply can't resist a pun, or is it because a certain someone says that nobody ever uses deque? ;)

Actually a deque would work better here since you are only taking off the end. vector would be preferrable if I didn't improve my first example by shuffling, as random access in a deque is done in linear time, not constant time.

Although I fear shuffling a deque might be slower.

Jeff

Instead of using if/else statements or switch/case statements to determine the card, why not create an enum type for the card's value? I remember in a C++ class I took, it was the professor's example for creating an enum.

Code:

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enum Value
{
One = 1,
Two,
Three,
Four,
Five,
Six,
Seven,
Eight,
Nine,
Ten,
Jack,
Queen,
King,
Ace
};

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Makes it a bit prettier to output that way. Ignore it if you like, I just always love a good enum.

I agree. An enum works well here. Then when you have a method to, say, get the numeric value of the card, the switch statement can reference Ten, Jack, Queen and King for value of 10 instead of integers.

Jeff

Jeff: I could argue that I foresaw a member function called cheat() that dealt off the bottom, but really I just liked the pun.

This got into quite the discussion... no, I don't need a hardcore, secure randomizer. I just want to shuffle a deck a little.

I've never used enum (I'm really a beginner, so I apologize for asking really basic question), so how does it work? do I put it outside all the functions and then it is accessible from deal() and it just treats it like a constant?

(and out of curiosity: what's a deque?)

Thanks everyone!
katy

a deque is a Double-Ended QUEue (pronounced "deck", hence the pun).

You can think of an enum as a way of declaring lots of constants in one go. there's a bit more to it than that but, at this stage, it'll do. I'm not sure that an enum provides too much value for money in this case (apart from what Jeff said about referring to Jack, etc, in the code), but it's not a bad idea to learn about them.

With a properly object-oriented design, you'll often find enums declared inside classes (it's also a work around for one of VC++'s many failings).

Code:

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class some_class
{
public:
    enum { relevant_constant1 = 1, relevant_constant2 = 17 };
    // etc;
};

// then refer to the values in code as:

if (some_value == some_class::relevant_constant1)
{
    // whatever
}

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Quote:

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Do you recommend deque because you simply can't resist a pun, or is it because a certain someone says that nobody ever uses deque?

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I guess you refered me for that someone. Once again you are putting words into my mouth. I am not God, I do not have the capability of surveying every walk of life on this planet to find out who uses what and who doesn't use what. Therefore I never make such assertions like "no body uses so and so" or "no body does so and so".

Read my lips! What I said was:
There is NOT a single thing in this world that any one can think of that can NOT be done WITHOUT using deque.

So there is this strange two-headed snake called deque. So what? Two-headed snakes do exist. Is that a big deal? What about three-headed snake?

Deque is a fancy invention. But I don't see it any more useful than a tri-que, quad-que, quant-que, or even deca-que, hexa-que. You can invent any thing you want. But it remains that anything that you do using deque CAN BE DONE WITHOUT it, with NO sacrifice of convenience or code efficiency or readability whatsoever.

Yeah. And all languages are equally powerful. There's no program that you can write in C++ that can't be written in FORTRAN or COBOL or PL1 or whatever. We don't need classes, recursion, bitwise operators, switch statements or any other paraphenalia of modern languages. All you need is a conditional statement, a loop construct that can be potentially infinite, a goto statement, somewhere to put your data and some basic manipulation methods. There is NOT a single thing in this world that anyone can think of that can NOT be done WITHOUT using C++. Now, anyone know where I can get a copy of masm?

Graham:

You know I talked bout deque in the context of C++ programming. I am not talking about lawyers or doctors using deque. I am talking about programmers doing C++ programming.

Can you tell me just one thing that using deque is superior than using other method? The mere fact that a lot of C++ programmer would ask "just what is deque" says how rarely deque is ever used at all.

Talking about assembly, it is a fact that this IT world can live without Java, or C++.net or VBScript or any other high level languages. But the IT simply can NOT live without the assembly language. It is as true as programming languages is useless without the existance of CPUs.

Well, if you're using a stack, would you rather use a vector instead of a deque ?

The point of deque is that when you use it, you know that you're only supposed to take stuff off the end (or beginning) and add stuff there. It is a self-imposed restriction that makes for nicer and better readable code.

Why do people write comments in their code ? They are totally useless, they are even ignored by the compiler ! Hum, weird, isn't it ?

I used deque recently for creating and undo/redo stack. It had everything I needed.

And Anthony, you do use definitives such as "always". It's one of the things I dislike most about your posts.

Quote:

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Therefore I never make such assertions

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Which is an assertion as well as false.

Jeff