使用共享任务结构并行计算π的OpenMP代码段

#include "stdafx.h"
#include 
#include 
#include 
using namespace std;
static long num_steps = 100000;
#define NUM_THREADS 2

void main(){
    int i;
    double x, pi, sum[NUM_THREADS];
    double step = 1.0 / num_steps;
    omp_set_num_threads(NUM_THREADS);
# pragma omp parallel private(i,x) shared(sum)
    {
        int id = omp_get_thread_num();
        sum[id] = 0;
# pragma omp for
        for (i = 0; i < num_steps; i++)
        {
            x = (i + 0.5)*step;
            sum[id] += 4.0 / (1.0 + x * x);
        }
    }
    for (i = 0, pi = 0; i < NUM_THREADS; i++)
        pi += sum[i] * step;
    printf("%f\n",pi);
}