Thread: C random number generator function...

I have made a function that generates a random number and, from that number, pulls a name from a list if criteria is met. BUT, I am questioning its capability. I know with computers, the numbers generated are more psuedo-random than "pure" random.

The function is:

Code:

int random(int copy_n, int n; char **names, char **save)
{
  int            i, max; 
  double       j;

  unsigned int   iseed = (unsigned int)time(NULL);
  srand(iseed);


  while(1){
      for(i = 0; i < n; ++i){
/*      Generate a random number between 0 and 1. */
        j = (double)(rand()/((double)RAND_MAX + 1));
//        printf ("The random number generated is %lf \n", j);
        if(j <= .1){
//          printf("---> Value of random number is less than");
//          printf(" or equal .1 with value of %lf.\n", j);
          strncpy(save[cap], names[i], 4);
          max += 1;
          if(max == copy_n){ // if max is equal to the amount to copy
                break;
          }
        }
      }

    if(cap == copy_n) break;

  }

  return 0;
}

so pass iseed in instead of doing it in the function?
any reason why it is bad to seed it in the function?

Well, I will be running it for multiple cases and want different lists. Thus, seeding the PRNG (psuedo-random number generator I assume you are referring to) with time. Its just that, although the lists are different, I am getting a common first id that appears to be not randomly generated.

Further, I only want to take the lower 10 % of the list. Thus, I generate a random number and if it is less then 10 %, copy the name to the save name list. Thus, don't want identical saved lists.

Originally Posted by laserlight

Seeding with time is fine. What I am talking about is not seeding more than once when you seed with time. Also, read Prelude's article on using rand().

Very interesting site... I see the use of "rand()/((double)RAND_MAX + 1)" there...

Since your code does not compile, I cannot tell if this is not merely a bug with your code.

No biggie... its not my full code, as that in itself is very long...

That does not "take the lower 10 % of the list". That just copies the current name to the save name list with about 10% of the time. The other 90% of the time, you just go on to the next iteration without doing anything else.

That is what I meant, sorry!