pthread_create用法，创建线程输出2*n

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

void *calculate(void * arg){
    int value = *(int *)arg;
    long value_2 = 2*(long)value;
    printf("The thread_id is %lu, created by %d\n", pthread_self(), getpid());
    sleep(1);
    return (void *)value_2;
}

int main()
{
    pthread_t pthread_buf;
    int n;
    //input a number n;
    printf("Please input a number n:");
    scanf("%d", &n);
    //创建一个线程
    pthread_create(&pthread_buf, NULL, calculate, &n);
    void *result;
    pthread_join(pthread_buf, &result);
    printf("the result of 2*n is : %ld\n", (long)result);


}