I'm trying to make this program to add 3 user inputed populations together. Here is a summary of what it is supposed to do and the code:

Code:
/*	Create the programs listed below per the specifications. You may not create any additional member function. Where listed, you must use the 
	declaration provided.

1.	Write a class called AssemblyLine. This class will be used to track the production of widgets. Each instance of the assembly line will 
	represent different assembly lines that are owned across the US. Create three instance of the AssemblyLine class to represent the factories 
	in Rochester, Fargo, and Nelson. Create a fourth instance that will sum up all the other instances. Create the following member functions:
a.	Two constructors. 
b.	An input member function
c.	An output member function
d.	A function that will take other AssemblyLine instances and add them together. You must use the following declaration:
	void Addit(AssemblyLine AL1)
e.	One of the member functions must be externally defined.*/
#include <iostream>
using namespace std;
///////////////////////////////////////////////////////////////////////////////////
class AssemblyLine
{
private:
	int widgets, total;
public:
	AssemblyLine() : widgets(0)
	{  }
	AssemblyLine() : total(0)
	{  }

	void Input()
	{
		cout << "Enter number of widgets: ";
		cin >> widgets;
	}
	void Output()
	{
		cout << "You entered: " << widgets;
	}
	void Addit(AssemblyLine AL1);
};
////////////////////////////////////////////////////////////////////////////////////
	void Addit(AssemblyLine AL1)
	{
		int pop1, pop1, pop3;
		cout << "Total population is: " << AL1 = pop1 + pop2 + pop3;
	}
////////////////////////////////////////////////////////////////////////////////////
int main()
{
	AssemblyLine Rochester, Fargo,  Nelson, Total;
	Rochester.Input();
	Rochester.Output();
	Fargo.Input();
	Fargo.Output();
	Nelson.Input();
	Nelson.Output();
	
	Addit(Total);

	int x;
	cin >> x;
	return 0;
}
I know this isn't right but I need a little guideline to get me on the right track to make this right.