我的Github地址：
9-0. Compile, execute, and test the programs in this chapter.
Ans：见Github。
9-1. Reimplement the Student_info class so that it calculates the finalgrade when reading the student's record, and stores that grade in the object. Reimplement thegrade function to use this precomputed value.
Ans：见Github。
9-2. If we define the name function as a plain, nonconst member function, what other functions in our system must change and why?
Ans：我们只须要改动函数 compare()的參数类型就可以：将原先的bool compare(const Student_info& x,const Student_info& y)改为
bool compare(Student_info x,Student_info y)
Tips：const对象不能够调用const成员函数函数。
为什么又把 Student_info& 改成了Student_info x？
由于sort(students.begin(),students.end(),compare)，函数中传递给compare是一个const对象，由于不能用一个const对象来初始化一个非const引用，故须要改动为传值形式。
9-3. Our grade function was written to throw an exception if a user tried to calculate a grade for aStudent_info object whose values had not yet been read. Users who care are expected to catch this exception. Write a program that triggers the exception but does not catch it. Write a program that catches the exception.
Ans：见Github。
9-4. Rewrite your program from the previous exercise to use thevalid function, thereby avoiding the exception altogether.
Ans：见Github。
9-5. Write a class and associated functions to generate grades for students who take the course for pass/fail credit. Assume that only the midterm and final grades matter, and that a student passes with an average exam score greater than 60. The report should list the students in alphabetical order, and indicate P or F as the grade.
Ans：见Github。
9-6. Rewrite the grading program for the pass/fail students so that the report shows all the students who passed, followed by all the students who failed.
Ans：见Github。
9-7. The read_hw function §4.1.3/57 solves a general problem (reading a sequence of values into avector) even though its name suggests that it should be part of the implementation ofStudent_info. Of course, we could change its name—but suppose, instead, that you wanted to integrate it with the rest of theStudent_info code, in order to clarify that it was not intended for public access despite its apparent generality? How would you do so?
Ans：见Github。