掌握系统调用fork()的使用方法及其功能；

利用系统调用sleep()调整父进程及各子进程的并发执行过程；

认真查看和比较每次执行结果，分析原因。

-Use to master the system call fork () function　use system calls the sleep () to adjust the parent process and child process concurrent execution of process　seriously view and compare each execution results, analyze the causes.