多线程计算PI代码c++

### 回答1：
以下是多线程计算PI的C代码：

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

#define THREADS_NUM 4
#define STEPS 100000000

double pi = .;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

void *calculate_pi(void *arg) {
int thread_id = *(int *)arg;
double sum = .;
int start = thread_id * STEPS / THREADS_NUM;
int end = (thread_id + 1) * STEPS / THREADS_NUM;

for (int i = start; i < end; i++) {
double x = (i + .5) / STEPS;
sum += 4. / (1. + x * x);
}

pthread_mutex_lock(&mutex);
pi += sum;
pthread_mutex_unlock(&mutex);

return NULL;
}

int main() {
pthread_t threads[THREADS_NUM];
int thread_ids[THREADS_NUM];

for (int i = ; i < THREADS_NUM; i++) {
thread_ids[i] = i;
pthread_create(&threads[i], NULL, calculate_pi, &thread_ids[i]);
}

for (int i = ; i < THREADS_NUM; i++) {
pthread_join(threads[i], NULL);
}

printf("PI = %.15f\n", pi / STEPS);

return ;
}

### 回答2：
多线程计算PI的代码可以如下所示：

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

#define NUM_THREADS 4
#define NUM_ITERATIONS 10000000

double sum[NUM_THREADS] = {0.0};

void *calculate_pi(void *thread_id) {
    long tid = (long)thread_id;
    int start = tid * NUM_ITERATIONS / NUM_THREADS;
    int end = (tid + 1) * NUM_ITERATIONS / NUM_THREADS;
    
    double result = 0.0;
    for (int i = start; i < end; i++) {
        double factor = 1.0 / (2 * i + 1);
        if (i % 2 == 0) {
            result += factor;
        } else {
            result -= factor;
        }
    }
    
    sum[tid] = result;
    pthread_exit(NULL);
}

int main() {
    pthread_t threads[NUM_THREADS];
    
    for (long t = 0; t < NUM_THREADS; t++) {
        int rc = pthread_create(&threads[t], NULL, calculate_pi, (void *)t);
        if (rc) {
            printf("Error: unable to create thread, %d\n", rc);
            exit(-1);
        }
    }
    
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }
    
    double pi = 0.0;
    for (int i = 0; i < NUM_THREADS; i++) {
        pi += sum[i];
    }
    pi *= 4.0;
    
    printf("PI: %f\n", pi);
    pthread_exit(NULL);
}

该代码使用多线程来计算PI的近似值。首先定义了4个线程和迭代次数为10000000。然后创建4个线程，并将计算PI的函数分配给每个线程执行。每个线程计算自己负责的一部分迭代，最后将结果存储在全局数组sum中。主线程等待所有线程完成后，将各个线程的结果累加起来，并进行一些计算得到PI的近似值。最后打印出PI的值。

### 回答3：
多线程计算PI的c代码如下：

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

#define NUM_THREADS 4 // 线程数量
#define STEPS 1000000 // 迭代次数

double pi = 0.0; // PI的结果
double step; // 每次迭代的步长

// 线程函数
void *calculatePI(void *param) {
    int thread_id = *(int*)param; // 获取线程ID
    int start = thread_id * STEPS / NUM_THREADS; // 计算起始迭代位置
    int end = (thread_id + 1) * STEPS / NUM_THREADS; // 计算结束迭代位置

    // 进行迭代求解
    double sum = 0.0;
    for (int i = start; i < end; i++) {
        double x = (i + 0.5) * step;
        sum += 4.0 / (1.0 + x * x);
    }

    // 将线程计算的结果加到全局变量pi中
    pi += sum * step;
    pthread_exit(NULL);
}

int main() {
    pthread_t threads[NUM_THREADS];
    int thread_id[NUM_THREADS];
    step = 1.0 / STEPS; // 计算步长

    // 创建多个线程进行计算
    for (int i = 0; i < NUM_THREADS; i++) {
        thread_id[i] = i;
        pthread_create(&threads[i], NULL, calculatePI, &thread_id[i]);
    }

    // 等待所有线程完成计算
    for (int i = 0; i < NUM_THREADS; i++) {
        pthread_join(threads[i], NULL);
    }

    // 输出最终结果
    printf("PI = %.15f\n", pi);

    return 0;
}

以上代码使用多线程方式计算PI的近似值。首先确定迭代次数和要使用的线程数量，然后通过线程函数进行迭代求解，将每个线程计算的结果加到全局变量pi中。主函数创建多个线程并等待它们完成计算，最后输出最终的PI近似值。