rand() weirdness

So, I'm debugging a bit of code that should work, but my computer hates me. What am I doing wrong?

In my main() function, I've got the simplest of loops:

Code:

for(int z = 0; z < nGenerations; z++)
    ParseData(nGridWidth, nGridHeight, dScore, gridInfo);

Then, a bit further along, I've got the offending function:

Code:

int ParseData(int nGridWidth, int nGridHeight, double dScore[], vector <vector <sGrid> >& gridInfo)
{
    int nCrossPoint;

    srand((unsigned)time(NULL));

    for(int j = 0; j < rand() % 25 + 1; j++)
    {
        rand();
    }
    
    for(int i = 0; i < nGridWidth / 2; i++)
    {
        nCrossPoint = rand() % nNumGenes;
        cout << nCrossPoint << endl;
    }

    return 0;
}

Here's the problem: The first time the function ParseData() is called, everything seems to be working fine. I get a set of (pseudo)random numbers that are good enough for my purposes. However, every subsequent call to the function gives me the same sequence of numbers. I could call the thing 10,000 times, and still get the same results. What's up with that?

You may want to read Prelude's article on Using rand(), in particular the section on seeding the PRNG.

http://c-faq.com/lib/srand.html

Note also that it's rarely useful to call srand more than once during a run of a program; in particular, don't try calling srand before each call to rand, in an attempt to get ``really random'' numbers.

Thank you both for your prompt replies. I always enjoy a bit of good late-night reading.

This is one of those situations when you know it's time to turn off the computer and pack it in for the night. Of course it was doing what it was doing...