1、数字存取：通过随机数函数产生50个正整数，逐个将这些数写入文件file.dat中；然后读出这些数，在内存中对它们进行排序，再将排序后的数据逐个写入file.out文件中。

要求：分别使用字节流和字符流操作方式完成。

2、文件内容加行号：给定一个文件，通过文件读写，给文件内容加行号。

要求：使用缓冲流操作。

3、学生对象操作：设计学生类，把学生对象存储进文件，并能再从文件中读取。-Digital access: 50 positive integer random number function, and one by one the number is written to the file file.dat　then read these numbers, sort them in memory, and then sorted the data one by one write into file.out file. Requirements: byte stream and character stream operation is completed. 2, the contents of the file add line numbers: given a file by file read and write, add line numbers to the contents of the file. Requirements: buffer stream operations. Students object operation: design students in the class, students object stored in the file, and read from the file again.