Calculate Pi Multi-thread

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
#include <pthread.h>
const int NUM_THREADS = 4;
 clock_t start, end;

static int count = 0;
void* circle_cnt(void* loopTimes)
{   int times = 0;
    int loop = (int)loopTimes;

     for(int i=0;i<loop;i++)
    {
        double x=(double)rand()/((double)RAND_MAX);
        double y=(double)rand()/((double)RAND_MAX);
        double distance= 1.0*x*x+1.0*y*y;
        if(distance<=1) times++;
    }
    count = count + times;
    pthread_exit(NULL);
}
int main(int argc, char*argv[])
{
        pthread_t tid[NUM_THREADS];
    int n=atoi(argv[1]);
    int div = n/NUM_THREADS;
    double pi = 1.0;
    srand(time(NULL));
    start = clock();
    int i = 0;
    for (i = 0; i < NUM_THREADS; ++i)
    {
        //pthread_attr_t attr;
        //pthread_attr_init(&attr);
        pthread_create(&tid[i], NULL, circle_cnt, (void*) div);
    }
    for (i = 0; i < NUM_THREADS; ++i)
    {
        pthread_join(tid[i], NULL);
    }
    pi=4.0*count/n;
        end = clock();
        double exe_time = ((double)(end - start)) / ( (double)(CLOCKS_PER_SEC) );
    printf("Pi: %lf\n",pi);
        printf("Time: %g seconds", exe_time);

    return 0;
}