Not understanding the error message I'm getting - c++

Question

I doing a freind function program according to this book I have and I did a little of my own code to the program. I puzzle because I get this error message that the "room_num" is undeclared and intellisense identifier "room_num" is undefine. I need help in understanding why this is happen and how to fix it. Here is the code I have been working on for the passed three weeks.
#include "stdafx.h"
#include <iostream>
#include <iomanip>
using namespace std;
class HotelRoom
{
friend int Transfer( HotelRoom&, int);
private:
int room_num;
int transroom_num;
int room_cap;
int occup_stat;
double daily_rt;
public:
HotelRoom(int room, int roomcap, int occup, int transroom, double rate = 89.00);
~HotelRoom();
int Display_Number(); //Displays room number and add the method Display_Guest()
int Get_Capacity();
int Get_Status();
double Get_Rate();
int Change_Status(int);
double Change_Rate(double);
void Display_Guest();
};
HotelRoom::~HotelRoom()
{
cout << endl<<endl;
cout << "Guest in room "<<room_num << " has checked out." <<endl;
}
int HotelRoom::Display_Number()
{
return room_num;
}
int HotelRoom::Get_Capacity()
{
return room_cap;
}
int HotelRoom::Get_Status()
{
return occup_stat;
}
int HotelRoom::Change_Status(int occup)
{
occup_stat = occup;
if (occup > room_cap)
{
return -1;
}
else
return occup_stat;
}
double HotelRoom::Get_Rate()
{
return daily_rt;
}
double HotelRoom::Change_Rate(double rate)
{
daily_rt = rate;
return daily_rt;
}
int Transfer(HotelRoom& room_r1, int transroom)
{
//if guest transfers to different hotel room, room is vacant and transroom is now occupied
room_r1.room_num = room_r1.transroom_num;
return room_num;
}
int main()
{
cout<< setprecision(2)
<<setiosflags(ios::fixed)
<<setiosflags(ios::showpoint);
int room = 0;
int roomcap = 4;
int transroom;
int occup;
double rate = 89.00;
cout<<"\nEnter the room number: "<<endl;
cin>>room;
cout<<"\nEnter the amount of guest to occupy this room: "<<endl;
cin>>occup;
cout<<"\nThe guest has decided to transfer rooms"<<endl;
cout<<"\nEnter the room to transfer the guest to"<<endl;
cin>>transroom;
HotelRoom room1(room,roomcap, occup, transroom, rate ); //initialize the object
if (room1.Change_Status(occup) == -1)
{
cout<<"You have exceeded the room capacity"<<endl;
}
else
{
cout <<"\nThe room number is ";
room1.Display_Number();
cout<<"."<<endl;
cout<<"\nThe name of the primary guest is ";
room1.Display_Guest();
cout <<"."<<endl;
cout<<"\nThe number of guest in the room is "<<room1.Change_Status(occup)<<"." <<endl;
cout<<"\nThe daily rate for room "<<room<< " is "<<room1.Get_Rate()<<"."<<endl<<endl;
cout<<"\nYou have tranferred the guest from room"<<room1.Display_Number()<<"to" <<Transfer(room1,transroom)<<endl;
}
cout<<"\nRoom ";
room1.Display_Number();
cout<<" is vacant."<<endl;
system("PAUSE");
return 0;
}

Answer 1

The function Transfer is not a method of HotelRoom, still you are trying to access room_num in it as if it was. You need to specify which room_num of which HotelRoom instance you mean. Probably you meant return room_r1.room_num instead of return room_num.
Also in your Transfer function you never use the parameter transroom, instead you are using a transroom_num from room_r1. This is probably not what you want.
Finally you haven't implemented the constructor and DisplayRoom of HotelRoom. You should create a stubs, which do nothing or print warnings as long as you haven't implemented the methods properly, so you can at least compile and link the code.

Answer 2

Since you are a beginner I would just stick with member functions and class private variables until you get better at it.
As far as the error message, my guess is that inside the function you are using room_num does not have access to the private parts of the HotelRoom class. Notice I said guess, that's because you should copy and paste the text on the output window here so we can see what exactly is happening.

Answer 3

First, you have to identify that room_num is class member variable.
int Transfer(HotelRoom& room_r1, int transroom)
{
room_r1.room_num = room_r1.transroom_num;
//because room_num is not non class member variable, you have to write like below.
return room_r1.room_num;
//return room_num;
}
Secondly, you did not write definition HotelRoom::HotelRoom(int,int,int,int,double), HotelRoom::Display_Guest(void). So you have to write this constructor and function for avoiding error LNK2019.