Using rand() ina class

[graciano]

Hi!

I was building a simple example of a class that represents a "dice".
At this point i have:
Dice.h

#include <cstdlib>
#ifndef DICE_H
#define DICE_H
class Dice{
public:
	Dice(){
		faceup = ThrowDice();
	}
	int getFace(){
		return faceup;
	}
	int ThrowDice(){
		faceup = rand()%6+1;
		return faceup;
	}
private:
	int faceup;
};
#endif 

And i tested it with ...
game.cpp

#include <iostream>
#include <ctime>
#include "Dice.h"
using namespace std;
int main(){
	int i;
	Dice A, B;
	for(i=0; i<10; i++){
		A.ThrowDice();
		cout << A.getFace() << endl;
	}
}

The problem is that i get always the same numbers.
How can i make the number generation more random without complicating too mush (because that is not the main subject here)?

Showl i use srand ant time?!

Thanks

[jsmith]

srand( time( 0 ) );

as the first line in main().

[Bazzy]

I would suggest calling srand(time(0)) in the class constructor

[jsmith]

That would reseed the RNG every time a Dice was constructed and would go against the rule of seeding only once.

[Bazzy]

Not if done in this way:

class Dice
{
    static bool init;
    public:
        Dice()
        {
            if(!init) 
            {
                init = true;
                srand(time(0));
            }
            // ...
        }
    //...
};
bool Dice::init=false;

So the programmer can use the Dice class without calling srand

(Edit) What's wrong in seeding few times?

[jsmith]

It is recommended that the RNG be seeded only once to generate "better" RNGs.

The above works, though I still would advocate moving the srand() to main() because now only Dice can call srand() in the entire application (which might not be a problem for the above application, but then consider a larger application that has a Coin class and a Flip() method -- now does Dice init the RNG, or does Coin, or both, or neither?). I don't think it should be Dice's responsibility to do that. In a truly object oriented, flexible architecture I would allow the user to construct a Dice with a random number generator function (using rand() as the default) along the same lines as the random_shuffle() standard algorithm.

[graciano]

I will use srand() in main, because otherwise i will be running away from my initial idea.

One of this days, with a little more time, i will try adding a "shuffle" method to the class so that who decides to use the class as not to worry about about the way random numbers are generated.

Thanks again