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++;
    }
...

Course** arr=p_department->get_p_course();
arr = new Course*[count_course + 1];

void operator += (Department& p_department, const Course& c)
{
//...
    Course** arr=p_department.get_p_course();
    arr = new Course*[count_course + 1];
}

*p_department[i] += temp;

#define _CRT_SECURE_NO_WARNINGS
#ifndef DEPARTMENT_H
#define DEPARTMENT_H
#include "Course.h"
#include <iostream>
#include <string>
using namespace std;
 
class Department
{
    static Department* p_department;    
private:
    string name_department;
    long id_department; 
    Course** p_course; //Error C2143 syntax error: missing ';' before '*'
                                      //Error C4430 missing type specifier - int assumed. Note: C++ does not support default-int
                                      //Error C2238 unexpected token(s) preceding ';'   
    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);
    string get_name() const { return name_department; } 
    long get_id_department() const { return id_department; }
    int get_count_course() const { return count_course; }
    Course** get_p_course() { return p_course; } //Error C2143 syntax error: missing ';' before '*'
                                                                             //Error C4430 missing type specifier - int assumed. Note: C++ does not support default-int
                                                                             //Error    C2238 unexpected token(s) preceding ';'
    void set_count_course(int count_course) { this->count_course = count_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& c); //Error C4430 missing type specifier - int assumed. Note: C++ does not support default-int
                                                                                                                   //Error  C2143 syntax error: missing ',' before '&'
 
};
 
#endif

void operator += (const Course& c);

cout << "Please enter student details." << endl;
cout << "Name:";        
cout << "Code:";                        
cout << "Sex:";                     
cout << "Age:";
Student temp;
cin >> temp;

istream& operator >> (istream &is, Student& s)
{
    cout << "Please enter student details." << endl;
    cout << "Name:";
    is >> s.name_student;
    cout << "Code:";
    is >> s.id_student;
    cout << "Sex:";
    is >> s.sex_student;
    cout << "Age:";
    is >> s.age_student;
    return is;
}

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

void Course::operator-=(const Student & s)
{
    Student** temp = new Student*[count_student - 1];   
    int index = s.get_p_student() - *p_student;
    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]; //access violation reading location
    delete[] p_student;
    p_student=temp;
}

Student** get_p_student() const { return p_student; }

    int index = s.get_p_student() - *p_student;

class Course
{
    static Course* p_course;    
private:
    string name_course;
    long id_course; 
    Student** p_student;
    int count_student;      
public: 
    Student** get_p_student() const { return p_student; }   
    Student& operator [] (int index_student) { return *p_student[index_student]; }
};

class Student
{
    static Student* p_student;
private:
    string name_student;
    long id_student;
    char sex_student;
    int age_student;
    Course** p_course;
    int count_course;
    .
        .
        .
 
};

 int index = s.get_p_student() - *p_student;

*temp_course[j] -= *temp_student[k]; //это находится в College.cpp

Student* get_p_student() const { return p_student; }

void Course::operator-=(const Student & s)
{
    Student** temp = new Student*[count_student - 1];   
    int index = s.get_p_student() - *p_student;

Student* get_p_student() const { return p_student; }

class Student
{
    static 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();
    static Student* instance();
    ~Student();
    void set(string name_student, long id_student, char sex_student, int age_student); //function set
    string get_name_student() const { return name_student; }
    long get_id_student() const { return id_student; }
    char get_sex_student() const { return sex_student; }
    int get_age_student() const { return age_student; }
    Student* get_p_student() const { return p_student; }
    bool operator == (long id_student);
    void operator += (const Course& c);
    friend ostream& operator << (ostream &os, const Student* p_student);
    friend istream& operator >> (istream &is, Student& s);
    Course* operator [] (int index_course) { return p_course[index_course]; }
};