Question

Random Numbers

Asked by: ltzorger

Hi,
Forgive me if this has been answered before but I can not seem to find a good solution. I have a assignment that wants me to create a fraction quiz that is generated by random numbers. There is an array of 5 fraction sets. I have everything working and I always get a different numerator and denominator, well at least as randomly as possible, but my issue is I always get the same numerator and denominator. When I pause my program in-between fractions I get different numbers and all is well but I do not think that is the best method by far.
I have included the code to my random number generator and I understand that it works on the bases of time. Thanks for any help

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Asked On
2009-03-26 at 12:57:35ID24268926
Tags

C++ Random Numbers

Topics

C++ Programming Language

,

Microsoft Visual C++

Participating Experts
2
Points
250
Comments
7

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Answers

 

by: jkrPosted on 2009-03-26 at 13:13:33ID: 23994702

Well, a simple example would be

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
 
void main( void )
{
   int i;
 
   /* Seed the random-number generator with current time so that
    * the numbers will be different every time we run.
    */
   srand( (unsigned)time( NULL ) );
 
   /* Display 10 numbers. */
   for( i = 0;   i < 10;i++ )
      printf( "  %6d\n", rand() );
}
                                              
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by: waysidePosted on 2009-03-26 at 13:13:37ID: 23994704

I don't see the code...

 

by: jkrPosted on 2009-03-26 at 13:14:20ID: 23994711

 

by: ltzorgerPosted on 2009-03-26 at 13:25:14ID: 23994827

Sorry about the code it seem to nver work the first time.

Fraction MathProblem::randomGenerator()
{  
	int n,d;
	
    for(int index=0; index<20; index++)
	{
		srand((unsigned)time(0));
		n = (rand()%10)+1;
		d = (float)(rand()%10)+1;
	}
	return Fraction (n,d);
 
}
////call
for(int i = 0; i < MAXNUM; ++i)
	testArray[i]= MathProblem((MathProblem::randomGenerator()),(MathProblem::randomGenerator()));

                                              
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by: jkrPosted on 2009-03-26 at 13:28:38ID: 23994872

The problem is that you seed the generator each time in the loop - that will cause it to start with the same values again. Just use

                srand((unsigned)time(0));

once in the constructor of 'MathProblem'.

 

by: ltzorgerPosted on 2009-03-26 at 13:35:15ID: 31563223

Your the man, or woman no offense ment, thank you so much I was beating my head agaist the wall. Works like a charm. Now on to adding templetes, I might be back.:)Thanks again

 

by: ltzorgerPosted on 2009-03-26 at 19:48:45ID: 23997697

After retesting my code I noticed that once the first two array elements are populate with the random number I got all the same numbers from then on.
To fix this I put the time seed
srand((unsigned)time(0));
into my set problem function so it will change after each new question is answered and a new one displayed.
I still think the advice to move the seed was the best and I am still thankful.

20120131-EE-VQP-002

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