Thread: Seeding a Random Number Generator

Hi all,

I am trying to design a class named "aDie" to roll a die 6,000 times and print out the results. I have a random number generator class that I am using.

I would like for the method int inputSeed() to accept a user's seed and then pass it to the method void seed(int s) which in turn passes it to the method void setSeed(int s). However, the code I'm using now does not generate different random numbers according to the seed I'm inputting. Each time I enter a different seed I get the same 10 random numbers.

I know my for loop only runs 10 times...I did it that way to test the random number generation before I move on to other parts of the assignment.

I'm not exactly sure what I'm doing incorrectly. Can someone please help?
Any assistance is greatly appreciated.

My files:

Code:

#ifndef ARANDOMNUMBERGENERATOR_H
#define ARANDOMNUMBERGENERATOR_H

#include <iostream>

using namespace std;

class aRandomNumberGenerator
{
public:
	aRandomNumberGenerator(void);
	void setSeed (int);//sets seed
                double generate ();//generates rand num using seed
	~aRandomNumberGenerator(void);
private:
                int seed;//private, modified by setSeed
};

#endif

Code:

#include "aRandomNumberGenerator.h"

#include <stdlib.h>

aRandomNumberGenerator::aRandomNumberGenerator(void)
{
     seed = 0;
}

void aRandomNumberGenerator::setSeed (int s) 
{
     seed = s;
     srand(seed);
}
double aRandomNumberGenerator::generate()
{	 
     return rand();
}

aRandomNumberGenerator::~aRandomNumberGenerator(void)
{

}

Code:

#ifndef ADIE_H
#define ADIE_H

#include <iostream>

#include "aRandomNumberGenerator.h" //a RandomNumberGenerator class declaration

using namespace std;

class aDie
{
public:
	aDie(void);
	int inputSeed();
	void seed(int s);
	~aDie(void);
private:
	int users_seed_input;
	int roll_count;
};

#endif

Code:

#include <iostream>
#include <iomanip>

#include "aDie.h"
#include "aRandomNumberGenerator.h"

using namespace std;

aDie::aDie(void)
{
	
}

// accepts seed from user
int aDie::inputSeed()
{
     cout <<"PLEASE ENTER A SEED FOR THE DIE: ";
     cin >> users_seed_input;
     cout <<"\nYOU ENTERED: " << users_seed_input <<endl; 
     //returns the seed entered by the user
     return 0;
}

void aDie::seed(int s)
{
	users_seed_input = s;
	aRandomNumberGenerator r;
	r.setSeed(users_seed_input);
}


aDie::~aDie(void)
{
	
}

Code:

#include <iostream>
#include <iomanip>
#include <cstdlib>

#include "aDie.h"
#include "aRandomNumberGenerator.h"

using namespace std;

int main(void)
{
	aDie mydie;
	aRandomNumberGenerator myrng;

	mydie.inputSeed();
	

	for(double i = 0; i<10; i++) //loop to print the 10 random numbers
	{
	cout << myrng.generate() << endl; //print each number on a new line
	}

	

	

	getchar();
	getchar();

	return 0;
}

I would like for the method int inputSeed() to accept a user's seed and then pass it to the method void seed(int s)

You should probably do that then.

Soma

Originally Posted by girly_engineer

However, the code I'm using now does not generate different random numbers according to the seed I'm inputting. Each time I enter a different seed I get the same 10 random numbers.

Considering that you are using the same seed every time you run the program, you find that surpising?

Code:

int aDie::inputSeed()
{
     cout <<"PLEASE ENTER A SEED FOR THE DIE: ";
     cin >> users_seed_input;
     cout <<"\nYOU ENTERED: " << users_seed_input <<endl; 
     //returns the seed entered by the user
     return 0;
}

this returns 0 not the "seed entered by user." Did you mean to do.

Code:

return users_seed_input;

Your comment // makes it appear that way, but that confuses me because when you call.

Code:

mydie.inputSeed();

you don't attempt to assign its value to anything else.

Secondly You don't ever Call

Code:

void aDie::seed(int s)

Which makes it look like S never gets defined a value. If you would change inputSeed() to a void and notice that this already assigns value to users_seed_input. You could Remove the line

Code:

users_seed_input = s;

and take the "int s" out of void aDie::seed(int s). And it seems like it would then work properly. Then when calling mydie.

Code:

mydie.inputSeed();
mydie.seed(); 

for(double i = 0; i<10; i++) //loop to print the 10 random numbers
{
  cout << myrng.generate() << endl; //print each number on a new line
}

Or you could leave it as a int function and when you call it try.

Code:

mydie.seed(mydie.inputSeed());

I'm still a beginner programmer too so I might have missed something. Hope this helps ;o).

And I did miss something! You seed the randomgerator class R (even though you didn't actually seed this class), but had you done so correctly you are still calling a different version of the class during your main.... which has not been seeded. . you might want to prevent calling a class during your other class function and just use logic of your class fuctions to call it during main.

Code:

myrng.setSeed(mydie.inputSeed());

that would also make your aDie::Seed function useless and you could delete it.

Just a note: srand() and rand() can only generate single streams of random numbers.

This means when you create another instance of that random number generator class, it's going to mess up the instance you created earlier!

If you're interested in generating multiple discrete streams of random numbers I recommend making a class using the Mersenne twister random number generator: Mersenne twister - Wikipedia, the free encyclopedia