C++/OpenMP error in rand

That's my code that should count Pi with monte Carlo method. We give in input: thread_count - number of processor threads, n - number of random generated points. Here's my code below

using namespace std;

int main (int argc, char* argv[]) {
/*sprawdzanie danych: thread_count - liczba wątków, n - liczba punktów*/
if (argc != 3) {
    cout << "Co Ty piszesz!. Ma być: ./pi <thread_count> <n>" << endl;
    exit(-1);
}

/*Sprawiamy by liczby były całkowite*/
int thread_count = atoi(argv[1]);
long n = atoi(argv[2]);

/*Test wartosci liczb*/
if (thread_count <= 0 || n <= 0) {
    cout << "Co Ty piszesz!. Ma byc większe od 0" << endl;
    exit(-1);
}
unsigned ziarno;
double x, y;
long int Ustrzelone = 0;
double Start = omp_get_wtime();
#pragma omp parallel default(none) private(x,y, ziarno) firstprivate(n) reduction(+:Ustrzelone) num_threads(thread_count) 
{
    ziarno = 25231 + 16*omp_get_thread_num();

    #pragma omp for schedule(dynamic)
    for(long i = 0; i <= n; i++) {
        x = (double) rand_r(&ziarno)/RAND_MAX * 2 - 1;
        y = (double) rand_r(&ziarno)/RAND_MAX * 2 - 1;

        if ((x*x) + (y*y) <= 1.0) {
            Ustrzelone += 1;
        }
    }
}

double Stop = omp_get_wtime();

double czas_obliczen = 1000 * (Stop - Start);

/*Ustawienie ilosci liczb po przecinku i wyswietlenie wyniku*/
cout.precision(15);
//double pi = (double) 4*Ustrzelone/n;
//cout << "Pi wynosi " << pi << endl;
cout << czas_obliczen << endl;

return 0;

In output I get error like that: [Error] 'rand_r' was not declared in this scope Not have much time left for this so hope you can bring me to some conclusion how to make it better.

Thank in advance.