Using dynamic allocation to create an array and insert elements into it

Question

I want to make a library management system as an assignment

class student
{
          char ID_number[30];
          char Student_name[30];
      public:
          void create_student()
          {
                    cout<<"\nEnter The ID Number ";
                    cin>>ID_number;
                    cout<<"\n\nEnter The Name of The Student: ";
                    cin>>Student_name;

                    cout<<"\n\nStudent Created Successfully"<<endl;
          }
          void show_student()
          {
                    cout<<"\nID Number: "<<ID_number;
                    cout<<"\nStudent Name: ";
                    cin.getline(Student_name,30);


          }

How would i go about using dynamic allocation to make every new entry go into an array and use pointers to show a certain student?

I am really bad at this particular part, thanks in advance!

Answer 1

Since you are coding in C++, and not in C, I would suggest using a string class, like std::string, instead of raw char arrays, e.g.:

std::string student_name;

If you want to store a list of students in memory, I'd suggest using the std::vector container, e.g.:

std::vector<Student> students;

You can use the vector::push_back method to add new students to the container.

---

EDIT If you want to use new[] and delete[] as a learning exercise, you may allocate a big array of students, and then use an integer index inside the array, pointing to the first free slot for inserting new students. E.g.:

int capacity = 100;
Student* students = new Student[capacity];

int student_count = 0;

To add a new student, you copy it in the array index given by student_count, and then you increment this variable by one, pointing to the next free slot in the pre-allocated array.

You must pay attention to not overflow the capacity of the array. Once the pre-allocated array is full, if you want to add a new student you need to allocate a new array with bigger capacity. You can use a 2x or 1.5x scale factor to calculate the new capacity.

Dont't forget to release the memory previously allocated with delete[].

If you do that, you are basically kind of implementing std::vector from scratch (even if this standard container has additional advanced features, like move semantics, etc.).

Answer 2

If by dynamic you mean you want to create "a few" stduent records, but aren't sure how many you don't need to worry about new or delete. Just use a vector.

std::vector<student> students;
while(!bored)
{
    student latest;
    latest.creat_student(); // this looks a bit odd, perhaps it should be a free function...
    vector.push_back(latest);
    //TODO - see if I am bored yet
}

Now we have students. You said you wanted to use pointers to display them. Or rather a certain student. You haven't described how you will choose a "certain student", so let's show them all first

for (auto item : students)
{
    item.show_student();
}

Disappointingly, your show_student method isn't declared const, which you should consider.

To index to a particular student, you could use students[17]. Or which ever index you want. You might be able to use std algorithms to find students with particular properies, if you provide a way to get the properties (and of course consider using std::string instead of char *)

---

If you really want to use a raw array of student, then something like this works, but you will get into reallocs etc if 5 or whatever you choose isn't enough. Which is a compelling reason for choosing a std::vector.

student * them = new student[5];
for (size_t i = 0; i < 5; ++i)
{
    student latest;
    latest.create_student();
    them[i] = latest;
}

for (size_t i = 0; i < 5; ++i)
{
    them[i].show_student();
}
delete[] them;

Answer 3

std::vector<student> or std::vector<student*> if you want a pointer.

Adding a new student :

Student* newStudent = new Student(name);

vector.append(newStudent);

Reading a student called "Victor" and then deleting it:

Student* victor;
for(int i = 0; i<vector.size();i++) {
    if(vector.at(i)->getName() == "Victor") {
        victor = vector.at(i);
        break;
    }
 }
//Then you can delete it
delete(victor);

std::vector