实现7个功能，即显示所有学生缺课记录，录入学生缺课信息，查询某个学生缺课情况，修改缺课记录，删除缺课记录，统计某段时间缺课记录，退出系统。程序运行调试正常。-Achieve 7 function, which displays all students absent school records, recording student absenteeism, query a student absences, absences modify records, delete records ab