说明：  一个学生类，包括数据成员姓名、分数、等级（字符型数组），设计友元函数，用来根据成绩分数确定对应的等级：90~100：优； 80~89：良； 70~79：及格； 60以下：不及格； disp()成员函数用来显示学生的数据。主函数中定义学生类对象数组，初始化姓名和分数；输出结果；显示每个学生的姓名、分数、等级。
(A student categories, including data members names, scores, class (character array), the design of the Friends of element function, used to determine the basis of merit scores of the corresponding level: 90 ~ 100: excellent 80 ~ 89: good 70 ~ 79: pass 60 the following: failure disp () member functions of the data used to show students. The main function of the object type defined in the array of students, name and scores of initialization output shows the names of each student, scores, grade.)