第四题（迅雷笔试题）：编写一个程序，开启3个线程，这3个线程的ID分别为A、B、C，每个线程将自己的ID在屏幕上打印10遍，要求输出结果必须按ABC的顺序显示；如：ABCABC….依次递推。

#include <iostream>
#include <stdlib.h>
#include <pthread.h>
using namespace std;

pthread_mutex_t myloack=PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t mycond=PTHREAD_COND_INITIALIZER;
int n=0;
void *ThreadFunc(void *arg)
{
    int num=(int )arg;
    for (int i = 0; i < 10; ++i)
    {
        pthread_mutex_lock(&myloack);
        while (n!=num)
            pthread_cond_wait(&mycond,&myloack);

        if (num==0)
            cout<<"A";
        else if(num==1)
            cout<<"B";
        else
            cout<<"C"<<endl;
        n=(n+1)%3;
        pthread_mutex_unlock(&myloack);
        pthread_cond_broadcast(&mycond);
    }
    return (void *)0;
}
int  main(int argc, char const *argv[])
{
    pthread_t id[3];
    for (int i = 0; i < 3; ++i)
    {
        int err=pthread_create(&id[i],NULL,ThreadFunc,(void *)i);
        if (err!=0)
        {
            cout<<"create err:"<<endl;
            exit(-1);
        }

    }

    for (int i = 0; i < 3; ++i)
    {
        int ret=pthread_join(id[i],NULL);
        if (ret!=0)
        {
            cout<<"join err:"<<endl;
            exit(-1);
        }
    }
    return 0;
}