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Random no. function dispays the same number

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Join Date: Apr 2009

Posts: 147

Reputation: gretty is an unknown quantity at this point

Solved Threads: 7

gretty

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Junior Poster

Random no. function dispays the same number

Aug 2nd, 2009

hi

My random number function is meant to loop 6 times & output 6 different numbers. But instead it outputs 6 of the same numbers. How do I fix it?

Any advice would be really helpful.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <string>
 
 
using namespace std;
 
int random(int max)
{
	srand(time(NULL));
 
	return ((rand()%max)+1);
}
 
int main() 
{
 
for (int i=0; i<6; i++) {
		used_nos[i] = random(40);
		cout << used_nos[i] << endl;
	}
 
return 0;
}
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <string>


using namespace std;

int random(int max)
{
	srand(time(NULL));

	return ((rand()%max)+1);
}

int main() 
{

for (int i=0; i<6; i++) {
		used_nos[i] = random(40);
		cout << used_nos[i] << endl;
	}

return 0;
}

Last edited by gretty; Aug 2nd, 2009 at 5:05 am.

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Join Date: May 2007

Posts: 1,868

Reputation: twomers has a spectacular aura about

Solved Threads: 56

twomers

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Posting Virtuoso

Re: Random no. function dispays the same number

Aug 2nd, 2009

I'd imagine if you were to wait in the for loop for about a second per iteration it'd be different.

The problem is that you're reseeding the rand function so quickly it's being reseeded off the same value. You only need to seed it once, so do it at the start of main.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <string>
 
 
using namespace std;
 
int random(int max)
{
 
	return ((rand()%max)+1);
}
 
int main() 
{
 
	srand(time(NULL));
for (int i=0; i<6; i++) {
		used_nos[i] = random(40);
		cout << used_nos[i] << endl;
	}
 
return 0;
}
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <ctime>
#include <iomanip>
#include <string>


using namespace std;

int random(int max)
{

	return ((rand()%max)+1);
}

int main() 
{

	srand(time(NULL));
for (int i=0; i<6; i++) {
		used_nos[i] = random(40);
		cout << used_nos[i] << endl;
	}

return 0;
}

For further clarification... srand takes time(null) in your code, which updates every second, I believe. So if srand was in the function and if the loop executed for over a second you'd get different numbers out every different second.

Last edited by twomers; Aug 2nd, 2009 at 5:32 am.

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