Question

这是一个必须使用动态创建的Course数组完成的类赋值。我试图在我的for循环内部读入每个成员变量，但我不确定如何做到这一点。我用我的学生结构做了这个，但是这个数组的不同之处让我搞砸了，因为我不知道如何继续它。

尝试读取struct成员时，我的问题出在readCourseArray函数中。如果有人能告诉我我是怎么做的，我会很感激。我知道使用new运算符并不理想，许多指针都是不必要的，但这只是我的指导员要求分配的工作方式。

#include <iostream>
#include <string>
using namespace std;

struct Student
    {
        string firstName, lastName, aNumber;
        double GPA;
    };
struct Course
    {
        int courseNumber, creditHours;
        string courseName;
        char grade;
    };

Student* readStudent();
Course* readCourseArray(int);
int main()
{
    int courses = 0;
    Student *studentPTR = readStudent();
    Course *coursePTR = readCourseArray(courses);


    delete studentPTR;
    delete coursePTR;
    system ("pause");
    return 0;
}

Student* readStudent()
{       Student* student = new Student;
    cout<<"\nEnter students first name\n";
    cin>>student->firstName;
    cout<<"\nEnter students last name\n";
    cin>>student->lastName;
    cout<<"\nEnter students A-Number\n";
    cin>>student->aNumber;


    return student;
}

Course* readCourseArray(int courses)
{
    cout<<"\nHow many courses is the student taking?\n";
    cin>>courses;
    const int *sizePTR = &courses;
    Course *coursePTR = new Course[*sizePTR]; 

    for(int count = 0; count < *sizePTR; count++)  //Enter course information
    {
        cout<<"\nEnter student "<<count<<"'s course name\n";
        cin>>coursePTR[count]->courseName>>endl;
        cout<<"\nEnter student "<<count<<"'s course number\n";
        cin>>coursePTR[count]->courseNumber;
        cout<<"\nEnter student "<<count<<"'s credit hours\n";
        cin>>coursePTR[count]->creditHours;
        cout<<"\nEnter student "<<count<<"'s grade\n";
        cin>>coursePTR[count]->grade>>endl;
    }


    return coursePTR;
}

Answer 1

数组下标运算符返回数组的一个元素。

coursePTR[count]相当于将指针递增到数组的开头并取消引用结果，例如：*(coursePTR + count)。你得到的是Course类型的对象（或对一个的引用）。所以你需要使用'dot'运算符，而不是'arrow'运算符来访问元素：

cin >> coursePTR[count].creditHours;

你还有另一个错误：

cin >> coursePTR[count].courseName >> endl;
                                      ^^^^

这不会编译。 endl只能用于输出流。

Answer 2

Course* readCourseArray(int &courses);    // Update the definition to pass "courses" by reference.

Course* readCourseArray(int &courses)    // Pass the courses by reference so that your main() has the value updated.
{
    cout<<"\nHow many courses is the student taking?\n";
    cin>>courses;
    /*
        You don't need this line.
    */
    // const int *sizePTR = &courses;

    /*
        You've allocated space for "courses" no. of "Course" objects.
        Since this is essentially an array of "Course" object, you 
        just have to use the "." notation to access them.
    */
    Course *coursePTR = new Course[courses]; 

    /*
        "endl" cannot be used for input stream.
    */
    for(int count = 0; count < courses; count++)  //Enter course information
    {
        cout<<"\nEnter student "<<count<<"'s course name\n";
        cin>>coursePTR[count].courseName;
        cout<<"\nEnter student "<<count<<"'s course number\n";
        cin>>coursePTR[count].courseNumber;
        cout<<"\nEnter student "<<count<<"'s credit hours\n";
        cin>>coursePTR[count].creditHours;
        cout<<"\nEnter student "<<count<<"'s grade\n";
        cin>>coursePTR[count].grade;
    }

    return coursePTR;
}

读入动态创建的指向结构数组的指针

2 个答案: