学生名单自己创建，名单至少包括学号，姓名，班级3项信息，并保存到myfile.dat 中，程序在读取名单并显示时，不但支持单关键字排序，也支持第一键字，第二关键字排序。比如，仅按照学号排序，称为单关键字排序；在按照班级排序的情况下，再按照学号排序，称为双关键字排序。-Create your own list of students, including student id, name list at least three information, class, and save to myfile. Reading, the program landuse-dat list and display, not only supports single keywords ranking first key word, also support, the second key word order. For example, according to the sequence, student id only single keyword sort, According to the class in the circumstances, sorting, called again according to the student id key word order. Double