题解 用C语言写的，vscode上能通过

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>  //线程库 pthread


#define THREAD_NUMBER 4 /* 线程数 */

void *thread_func(void* arg)
{
    int num =(long long)arg; /** sizeof(void*) == 8 and sizeof(int) == 4 (64 bits) */
    int res;
    int a[]={'A','B','C','D'};
    printf("%c", a[num]);
    pthread_exit(NULL);
}

int main()
{

    pthread_t thread[THREAD_NUMBER];
    int num, res;
    int t;
    /*输入进程执行的次数*/
    scanf("%d",&t);  

    /* 互斥锁初始化 */

    for(int i=0;i<t;i++){
        for (num = 0; num < THREAD_NUMBER; num++)
        {
            /*创建线程*/
            res = pthread_create(&thread[num], NULL, thread_func, (void*)(long long)num);
            /*创建失败*/
            if (res != 0)
                {
                    exit(res);
                }
            /*对应的线程结束后才返回，下个线程才能继续运行*/
           pthread_join(thread[num], NULL); 
        }

    }

return 0;
}