题目：有五个学生，每个学生有3门课的成绩，从键盘输入以上数据（包括学生号，姓名，三门课成绩），计算出

　　　 平均成绩，况原有的数据和计算出的平均分数存放在磁盘文件"stud"中。

-Topic: there are five students, each of the students has 3 course grades, from the keyboard input data above (including student number, name, three classes scores), calculated

Average grade, in original data and calculated the average scores of stored in the disk file "stud".