id  name       courses
     1  Wang  89.5  78.5  90.5
     2    Li  84.5  93.5  75.5
     3  Zhao  89.5  78.5  90.5

student1.GetGrade(course_name[0]) = 88.5

student1.GetAverageGrade() = 64.375

student1.ShowGrades(): 88.5 78.5 90.5

class1.ShowStudent(2): Li

class1.ShowStudentByIdOrder(by decending):
    id  name       courses
     3  Zhao  89.5  78.5  90.5
     2    Li  84.5  93.5  75.5
     1  Wang  89.5  78.5  90.5

StudentClass::showStudentCount(): 3