a)　　运行程序后显示以下信息：1、Display all information

2、Add a student

3、Delete a student

4、Quit

b)　　按1后进行简单数据处理并输出所有信息，输出的信息包括: 序号、学生姓名、学号、三门课的成绩、该学生的平均成绩、总成绩；并在最后计算每一门课程的平均成绩。

c)　　按2选择增加学生信息，学生数量最多为50，超过之后无法输入。输入信息包括学生姓名、学号、三门课程成绩（在程序中可以事先初始化几个学生信息）。

d)　　按3删除学生信息，根据输入序号删除对应的学生信息，序号从0依次往后排，当删除中间的学生信息后，将该序号后的学生信息依次往前移。

e)　　每次处理完之后继续显示之前的信息，可以再次按键进行操作。

f)　　按4退出程序。

-a) After running the program displays the following information: 1, Display all information 2, Add a student 3, Delete a student 4, Quit b) by 1 after a simple data processing and output of all information, the output information include: serial number, student' s name , student number, three classes of grades, the student' s grade point average, a total score　and the average score in the final calculation of each course. c) Press 2 to choose to increase student information, the number of students up to 50, you can not enter more than after. Input information includes the student' s name, student number, three courses achievements (in the program can be pre-initialized several student information). d) Press 3 to delete student information, student information input according to delete the corresponding number, serial number sequentially　0 next row, after deleting the middle of the student information, the serial number after the student information sequentially moved forward