Error C2106: '=' : left operand must be l-value

class Department
{
    static Department* p_department;    
private:
    string name_department;
    long id_department; 
    Course** p_course;
    int count_course;
    Department(const Department& d);
    void operator = (const Department& d);
public: 
    Department();
    static Department* instance();
    ~Department();  
    void set(string name_department, long id_department);
    long get_id_department() const { return id_department; }
    int get_count_course() const { return count_course; }
    Course** get_p_course() { return p_course; }
    friend ostream& operator << (ostream &os, const Department* p_department);
    friend istream& operator >> (istream &is, Department* p_department);
    friend void operator += (Department* p_department,const Course& temp);
 
};

void operator += (Department* p_department, const Course& temp)
{
    int count_course = p_department->get_count_course();
    if (!count_course)
    {
        p_department->get_p_course() = new Course*[count_course + 1]; //здесь выдает ошибку
        p_department->get_p_course()[0] = Course::instance();
        cin >> p_course[0];
        count_course++;
    }
...

class Student
{
    Student* p_student;
private:
    string name_student;
    long id_student;
    char sex_student;
    int age_student;
    Course** p_course;
    int count_course;
    Department* p_department;
    Student(const Student& s);
    void operator = (const Student& s);
public:
    Student();
    Student* instance();
    ~Student(); 
    Student* get_p_student() const { return p_student; }}

Student* get_p_student() const { return p_student; }

Student* instance();

Student* p_student;

&s

case 1: //Add department
            {               
                if (!count_department)
                {
                    p_department = new Department*[count_department + 1];
                    Department temp_department;
                    cin >> temp_department;
                    p_department[0] = &temp_department;                 
                    count_department++;
                }
                else
                {                   
                    Department** temp_p_department = new Department*[count_department + 1];
                    for (int i = 0; i < count_department; i++)
                    {
                        temp_p_department[i] = p_department[i];
                    }                   
                    Department temp_department;
                    cin >> temp_department;
                    p_department[count_department] = &temp_department;
                    for (int i = 0; i < count_department; i++)
                        if (temp_p_department[count_department]->get_id_department() == p_department[i]->get_id_department())
                        {
                            cout << "Error! This department already exists." << endl;
                            goto end;
                        }
                    p_department = new Department*[count_department + 1];
                    for (int i = 0; i < count_department + 1; i++)
                    {
                        p_department[i] = temp_p_department[i];
                    }
                    count_department++;
                    delete[] temp_p_department;
                }               
                cout << endl;               
            end:break;
            }

case 8: //Print department information
            {
                long id_department;
                bool flag = false;
                cout << "Please enter code of department:";
                cin >> id_department;
                for (int i = 0; i < count_department; i++)
                    if (id_department == p_department[i]->get_id_department())
                    {
                        cout << *p_department[i];
                        flag = true;
                    }
                if (!flag)
                    cout << "Error! This department does not exist.";
                cout << endl;
                break;
            }

ostream& operator << (ostream &os, const Department& p_department) //operator cout
{
    os << p_department.name_department << endl << p_department.id_department << endl;
    return os;
}
 
istream& operator >> (istream &is, Department& p_department) //operator cin
{
    cout << "Please enter department details." << endl;
    cout << "Name:";
    is >> p_department.name_department;
    cout << "Code:";
    is >> p_department.id_department;
    return is;
}

                    p_department = new Department*[count_department + 1];
                    Department *temp_department = new Department;
                    cin >> *temp_department;
                    p_department[0] = temp_department;                 
                    count_department++;

Student* Course::operator [] (int index_student) { return p_student[index_student]; }

void Course::operator -= ( const Student & s)
{
    Student** temp = new Student*[count_student - 1];   
    int index;
    for (int i = 0; i < count_student; i++)
    {
        if (p_student[i] == &s)     
            index = i;      
    }
    for (int i = 0; i < index; i++)
    {
        temp[i] = p_student[i];
    }
    for (int i = 0; i < count_student - 1; i++)
    {
        temp[i] = p_student[i + 1];
    }       
    delete p_student[index]; //здесь ошибка.все никак не могу понять как удалить
    p_student=temp;     
}

void Course::operator -= ( const Student & s)
{
    Student** temp = new Student*[count_student - 1];   
 
    for (int i = 0, j = 0; i < count_student; i++)
    {
        if (p_student[i] == &s) continue;
        temp[j] = p_student[i];
        ++j;
    }
 
    delete &s;
    delete[] p_student;
    p_student = temp;     
}

void Course::operator += ( Student & s) //operator += add Student to Course
{
    if (!count_student)
    {
        p_student = new Student*[count_student + 1];        
        p_student[0]=&s;        
        count_student++;        
    }
    else
    {
        for (int i = 0; i < count_student; i++)
            if (s == p_student[i]->get_id_student())
            {
                cout << "Error! This student already exists." << endl;
                return;
            }
        Student** temp_student = new Student*[count_student + 1];           
        temp_student[count_student] = &s;               
        p_student = new Student*[count_student + 1];        
        for (int i = 0; i < count_student + 1; i++)
        {
            p_student[i] = temp_student[i];         
        }
        count_student++;        
        delete[] temp_student;      
    }   
}

void Course::operator += ( Student & s) //operator += add Student to Course
{
    if (!count_student)
    {
        p_student = new Student*[++count_student];        
        p_student[0] = new Student(s);        
    }
    else
    {
        for (int i = 0; i < count_student; i++)
            if (s == p_student[i]->get_id_student())
            {
                cout << "Error! This student already exists." << endl;
                return;
            }
 
        Student** temp_student = new Student*[count_student + 1];
        temp_student[count_student] = new Student(s);               
 
        for (int i = 0; i < count_student; i++) temp_student[i] = p_student[i];         
 
        count_student++;        
 
        delete[] p_student;
        p_student = temp_student;      
    }   
}

Student *temp_student = new Student;
cin >> *temp_student;