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C++ Real rnadom numbers

Hi,
I need to generate a random number between two values. So far I have been using rand() but it's not actually random, I always get the same pattern which is causing inaccuracies in my program. I tried seeding srand(time(NULL)) but that causes the same number to be generated every time... I assume because my program runs to fast for time() to keep up?

anyway, I need a way of generating a real random number...

thanks.

AlexFM

srand( time( NULL ) ) is the way to initialize random time generator. Please show your code.

liseperu

ASKER

here is my code:

double random = 0.0;

srand(time(NULL));
random = (rand()%4);

AlexFM

I run the following program number of times and get different numbers from 0 to 3:

double random = 0.0;
srand(time(NULL));
random = (rand()%4);
cout << random << endl;

I guess you run this code in some loop and get the same results, like this:

for ( int i = 0; i < 10; i++ )
{
double random = 0.0;
srand(time(NULL));
random = (rand()%4);
cout << random << endl;
}

Solution is to call srand only once before loop:

srand(time(NULL));

for ( int i = 0; i < 10; i++ )
{
double random = 0.0;
random = (rand()%4);
cout << random << endl;
}

liseperu

ASKER

sorry, I should have put the whole function:

Neuron::Neuron(int noInputs, double Xcoord, double Ycoord, int noWeights,vector<vector<double> > data)
{
      _noInputs = noInputs;
      _Xcoord = Xcoord;
      _Ycoord = Ycoord;

      _noWins = 0;
      _winRate = 0;

      double random = 0;
      srand(time(NULL));
      for(int x = 0; x< noWeights; x++)
      {
            random = (rand()%254)+1;
            _weights.push_back(0.0);
      }

}

however, this is in the constructer of a class that is created in a for loop in another class . i.e.

for(int t = 0; t < _numberOfNeuronsPerLayer; t++)
{
      _neuronLayer.push_back(Neuron(noInputs, 0, t, noWeights,data));
}

which is created in a loop in another class!!

How about if I seed srand in main before I start the actual system?

ASKER CERTIFIED SOLUTION

AlexFM

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liseperu

ASKER

yep, that did it... thanks a lot for your help