一个学生成绩管理系统，可以添加、删除和修改学生信息和成绩，同时可以查找下一个，把数据库的数据在窗口显示出来-A student performance management system, you can add, delete and modify student information and grades, and can find the next one, the database data is displayed in the window

根据输入的学生学号、成绩，计算平均成绩，最高分、最低分-Enter two student id name and grades of students