trying to create private member array, with size given from initializer list in C++( usage is forbidden)

Question

So i'm trying to create a private member array on my School class where i'm going to be holding the address of some student objects. My goal is to simulate the stusents entering the school building if the capacity of the building allows as such (think of the problem with small numbers) I have managed to implement the "address object part" but i have an issue concerning the size of the array. The variable which gives the size of the array is also a private member of the same class. That being said the compiler gives the error:

error: invalid use of non-static data member ‘School::class_capacity’

148 | Student* pointer_array[class_capacity];

Here's School class:

class School
{
    private:
      int class_capacity;
      Student* pointer_array[class_capacity];
   public:
        School(const int capacity)//constructor
      :class_capacity(capacity)
      {
        cout << "A New School has been created!" << endl;
      };
      ~School(){//destructor
        cout << "A School to be destroyed!" << endl;
      }; 
      void enter(Student* student, int stc=0/*student counter*/);
}

Student class is :

class Student 
{
private:
    string name;
    int no_floor;
    int no_classroom;
public:
    Student(const string& nam,int no_fl,int no_cla)//constructor
    : name(nam), no_floor(no_fl), no_classroom(no_cla)
    {
      cout << "A new student has been created! with name " << name << " heading to floor: "<< no_floor << " class: " << no_classroom << endl;
    };

    ~Student()//destructor
    {
      cout << "A Student to be destroyed! with name " << name << " is at "<< " class: " << no_classroom;

    };

Lastly my main where i allocate an array of pointers to Student objects.

int main(void)
{
//Student creation
       int i,floor,classroom;
       string stname;
       Student* students[5];
       for(i=0; i<5; i++)
       {
          cin >> stname;
          cin >> floor;
          cin >> classroom;
          students[i] = new Student(stname, floor, classroom);
       }
       for(i=0; i<5; i++)
       {
         delete students[i];
       }
}

And the enter function code:

void School::enter(Student* student, int stc/*student counter*/)
{
  pointer_array[stc] = student;
  (pointer_array[stc])->print();
  cout << " enters school!" << endl;
}

The array i'm trying to create in School class is meant to keep a pointer to already created Student objects on my main.
Does anybody know how to solve this? Again library usage is forbidden

Answer 1

Without using std::vector you'd need to do your own dynamic array management

class School
{
private:
    int class_capacity;
    Student* students;
public:
    School(const int capacity)//constructor
      :class_capacity(capacity)
    {
        students = new Student[capacity];
        cout << "A New School has been created!" << endl;
    };

    ~School(){//destructor
        delete[] students;
        cout << "A School to be destroyed!" << endl;
    }; 

    // Disable copying to avoid accidental double-deletion of array
    School(School const&) = delete;
    School& operator=(School const&) = delete;
};

Answer 2

Student* pointer_array[class_capacity];

is not legal code since class_capacity is not known at compile time. You'll have to use a dynamically allocated array.

Use of std::vector<Student> will be appropriate most of the time. Since you are not allowed to use std::vector, your only option is to use

Student* student_array; // Not pointer_array.

as the member variable. Memory for the array can be allocated in the constructor.

   School(const int capacity) : class_capacity(capacity),
                                student_array(new Student[capacity]) {}

Please note that you need to follow The Rule of Three when you manage dynamic memory in your class.

---

Update, in response to OP's comment.

I would suggest adding a default constructor to Student.

// Default constructor, implemented using the other constructor.
Student() : Student("", 0, 0) {}

Answer 3

I finally managed to find the answer.The classes should look something like this.

School class:

class School
{
    private:
      int class_capacity;
      Student** pointer_array;
   public:
        School(const int capacity)//constructor
      :class_capacity(capacity)
      {
        pointer_array = new Student*[capacity];
        cout << "A New School has been created!" << endl;
      };
      ~School(){//destructor
        delete [] pointer_array;
        cout << "A School to be destroyed!" << endl;
      }; 
      void enter(Student* student, int stc=0/*student counter*/);
}

Class student , main and enter function stays as is.