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.txt"中。 -There are five students, each student has three classes of results, data from more than keyboard input (including student number, name, class 3 results), to calculate average scores, the status of the original data and calculated the average score storing in the disk file　stud.txt　in.