Reading into dynamically created pointer to array of structs

Question

This is a class assignment that must be done using a dynamically created array of Course. I am trying to read into each member variable inside of course inside of my for loop but I'm not really sure how to do it. I did it with my student struct but the difference in this being an array is messing me up because I'm not sure how to proceed with it.

My problem is in the readCourseArray function when trying to read in struct members. If anyone could tell me how I do that I'd be appreciative. I know using the new operator isn't ideal along with many of the pointers being unnecessary but it is just how my instructor requires the assignment to be turned in.

#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;
}

One immediate thing you should know is that in functions that return a pointer, you should not return a local variable. When you create a pointer in the function, it goes out of scope when the function ends and you end up with problems when you try to use that now-deceased data. When you use cin to read the variables, coursePTR [count] is treated like a normal variable, so use the . operator. You'd use the arrow on coursePTR. coursePTR [count] is already dereferenced since coursePTR [count] is read as *(coursePTR + count) — Qaz
– Qaz, Commented Feb 22, 2012 at 23:30

jrok · Accepted Answer · 2012-02-22 23:37:40Z

1

Array subscript operator return an element of the array.

coursePTR[count] is equivalent to incrementing the pointer to the start of array and dereferencing the result, like: *(coursePTR + count). What you get is an object (or a reference to one) of type Course. So you'll need to use 'dot' operator, not 'arrow' operator to access the elements:

cin >> coursePTR[count].creditHours;

You've got another error:

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

This won't compile. endl can only be used on output streams.

answered Feb 22, 2012 at 23:37

jrok

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vvnraman · Accepted Answer · 2012-02-22 23:40:41Z

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;
}

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