c语言教程2：结构体的运用。输入N个学生的姓名和其3门成绩，可执行功能：按平均成绩由高到低输出，按姓名由低到高输出，按学号查找，按姓名查找。(C language course 2: the use of the structure. Input N student names and 3 scores, executable functions: output from high to low according to the average score, and output from na