How to display a linked list that gets struct data as a data in c++?

I have this struct and I initialize it in my linked list class, but I am not sure how to display it:

struct CourseData {
    string CourseID, MaxCapacity, CurrentCapacity ;
    string CourseName, InstructorName, CourseSection, CourseLocation, ListOfStudents;
};

class CourseNode {
    private:
        CourseData elem;
        //
        CourseNode* next;

    public:
        CourseNode(CourseData elem) : elem(elem)
        {}  
        friend class Courses ;

};

class Courses {
    private:
        
        CourseNode *head;
    public:     
        Courses();
        ~Courses();

What should I change to this code? It outputs an error:

void Courses::display() const
{
    CourseNode *ptr=head;
    cout<<"Head->";
    while(ptr!=NULL)
    {
        cout<<ptr->elem<<"->";
        ptr=ptr->next;
    }
    cout<<"Null"<<endl;
}