Having problem in mutual friendship between the classes

I am new to C++.In order to learn this, I am making a phonebook application which uses C++ concepts and functionalities. I have made two classes, phonebook and features; the phonebook class uses all functions of features, and the features class uses functions of phonebook.

But, when I am trying to pass a features class object to phonebook functions as an argument, the compiler gives an error that "features is not a type".

Why this error is coming – features is a class here not a datatype? How can I resolve this issue?

Please see below code:

#include<stdlib.h>
#include<string.h>
#include<iostream>
#include<fstream>
#include<windows.h>
#include<iomanip>
#include<regex>

#define ADD_CONTACT         1
#define DELETE_CONTACT      2
#define EDIT_CONTACT        3
#define SHOW_CONTACT        4
#define DISPLAY_CONTACTS    5
#define SETTINGS            6
#define EXIT_MAIN           7
using namespace std;
class features;
//phone book page
class phonebook
{
//details of contact:

//mandatory details to store a contact
string first_name;
string last_name;
bool name_order;
string mobile_num;
string work_num;
string home_num;

//additional details for a contact
string company_name;
string job_title;
string email;
string location;
string dob;

bool favorite_flag;
bool friend_flag;
bool family_flag;
bool office_flag;
bool work_num_flag;
bool home_num_flag;
bool mobile_num_flag;
//flags of details whether present or not:
bool company_name_present=0;
bool job_title_present=0;
bool email_present=0;
bool address_present;
bool dob_present=0;
bool relation_present;
bool location_present=0;

//number of contact numbers present for each contact


//kind of number either work or home or mobile or telephone_home or telephone_office
int num_kind;

//link for linked list
phonebook* link;
        //bool allocate_mem_to(phonebook* &);

        bool check_number_valid(string &);
        bool check_email_valid(string &);
        void reverse_linked_list(phonebook* &);
        void add_in_sorted_order(phonebook* &,phonebook* &,bool,bool);
        void print_all_the_details(phonebook* &);
        friend void operator>>(istream&,phonebook*&);
        friend void operator<<(ostream&,phonebook*&);

    public:
        phonebook(){
            favorite_flag=0;
            friend_flag=0;
            family_flag=0;
            office_flag=0;
            mobile_num_flag=0;
            work_num_flag=0;
            home_num_flag=0;

            company_name_present=0;
            job_title_present=0;
            email_present=0;
            location_present=0;
            dob_present=0;
            relation_present=0;

            name_order=0;

            link=NULL;
        }
        ~phonebook(){}
        friend class features;
        void add_contact(phonebook* &,features obj);
        void delete_contact(phonebook* &,features obj);
        void edit_contact(phonebook* &,features obj);
        void show_contact(phonebook* &,features obj);
        void display_contacts(phonebook* &,features obj);
        void features();


        bool phonebook_login_operations();
};
class features
{
    bool sort_flag;
    bool name_order_flag;
    bool friends_display;
    bool family_display;
    bool office_display;
    bool all_contacts_display;
    bool only_favourites;

    public:

        friend class phonebook;

        features();

        ~features()
        {

        }
        void add_to_favourites(phonebook* &);
        void contacts_to_display();
        void sort_by();
        void name_order();
        void print_main_admin_menu();

};
void phonebook::add_contact(phonebook* &head,features obj)//Here complier gives error"features is not type"
{

    phonebook *temp_obj=NULL,*read_obj=NULL,*traverse_pointer=NULL;

    temp_obj=new phonebook;

    cin>>temp_obj;

    bool sort_flag_1=0;
    bool name_order_flag_1=0;

    ifstream file_in;
    file_in.open("phonebook_contacts.txt");
    if(file_in)
    {
        if(head==NULL)
        {
            if(obj->sort_flag == false)
            sort_flag_1=0;
            else
            sort_flag_1=1;

            if(obj->name_order_flag == false)
            name_order_flag_1=0;
            else
            name_order_flag_1=1;

        while(file_in)
        {
            read_obj=new phonebook;
            file_in.read((char*)read_obj,sizeof(*read_obj));


            add_in_sorted_order(head,read_obj,sort_flag_1,name_order_flag_1);

        }
        }

            add_in_sorted_order(head,temp_obj,sort_flag_1,name_order_flag_1);

        file_in.close();

        ofstream file_in_out;

        file_in_out.open("phonebook_contacts.txt");

        for(traverse_pointer=head;traverse_pointer;traverse_pointer=traverse_pointer->link)
            file_in_out.write((char*)traverse_pointer,sizeof(*traverse_pointer));

        file_in_out.close();
    }
    else
    {
        ofstream file_out;
        file_out.open("phonebook_contacts.txt");

        file_out.write((char*)temp_obj,sizeof(temp_obj));

        file_out.close();
    }

}