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-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 the ave