#include <stdio.h>
#include <pthread.h>

#define INTERVALS 100000
#define THREADS 4

float global_sum = 0.0;
pthread_mutex_t global_lock = PTHREAD_MUTEX_INITIALIZER;

void *pi_calc(void *num)
{
  float my_sum = 0.0;
  int myid = *(int*)num;
  float h = 1.0 / INTERVALS;
  int start = (INTERVALS / THREADS) * myid;
  int end = start + (INTERVALS / THREADS);

  float x;
  int i;
  for (i = start; i < end; i++)
  {
    x = h * ((float)i - 0.5);
    my_sum += x;
  }

  pthread_mutex_lock(&global_lock);
  global_sum += my_sum;
  pthread_mutex_unlock(&global_lock);
}

int main ()
{
  pthread_t tid[THREADS];
  int i;
  int t_num[THREADS];

  for (i = 0; i < THREADS;i++)
  {
    t_num[i] = i;
    pthread_create(&tid[i], NULL, pi_calc, &t_num[i]);
  }

  for (i = 0; i < THREADS; i++)
    pthread_join (tid[i], NULL);

  printf ("Sum = %f\n", global_sum);
}

#include <pthread.h>

int main (){
 ......
 ......
 pthread_t	our_thread_id;
 pthread_create(&our_thread_id,NULL,pi_calc,NULL); //Создаю поток

//прототип
void *pi_calc();

7void *pi_calc()
{
	           printf("functionA active\n");
		sleep(5);
		printf ("functionA is finished.\n");
		return(NULL);
}

void *pi_calc(void*arg)

           int id, result;
	pthread_t	our_thread_id;
	id = 1;
           result = pthread_create(&our_thread_id,NULL,&pi_calc,&id);
    	if (result != 0) {
         perror("Creating the first thread");
         return EXIT_FAILURE;
       }
..............
..............
          pthread_join(our_thread_id, NULL);
          pause();

#include <iostream>
#include <iomanip>
#include <stdio.h>
#include <stdlib.h>
#include <sys/neutrino.h>
#include <pthread.h>
#include <errno.h>
#include <sched.h>
#include <unistd.h>
#include <math.h>

#define INTERVALS 100000
#define THREADS 2


using namespace std;

double global_sum = 0.0;
pthread_mutex_t global_lock = PTHREAD_MUTEX_INITIALIZER;

void *pi_calc(void *);

int main ()
{
  pthread_t tid[THREADS];
  int i,result;
  int t_num[THREADS];

  for (i = 0; i < THREADS; i++)
  {
    t_num[i] = i;
    result = pthread_create(&tid[i], NULL, pi_calc, &t_num[i]);
    if (result != 0) {
     perror("Creating the thread");
     return EXIT_FAILURE;
    }
  }

  for (i = 0; i < THREADS; i++){
      result = pthread_join (tid[i], NULL);
      if (result != 0) {
                perror("Joining the first thread");
                return EXIT_FAILURE;
              }
  }
  cout<<"Результат : "<<setprecision(20)<< global_sum<< endl;
}

void *pi_calc(void *)
{
  double my_pi = 0.0;
  double h = 1.0 / INTERVALS;
  double x;
  int i;
  for (i = 1; i < INTERVALS; i++)
  {
    x = ((double)i - 0.5)*h;
    my_pi = my_pi+ 4.0 / (1.0 + x * x);
  }

  pthread_mutex_lock(&global_lock);
  global_sum = my_pi*h;
  pthread_mutex_unlock(&global_lock);
}