operator+ overloading

Hey, I'm trying to overload the assignment operator '+' to add two objects. I need to add throttle sample2 and throttle sample3.
I've tried several things and keep getting errors.

Here is what I am working on...

Code:

---

//Operator fxn outside class
#include <iostream>
#include <cstdlib>
using namespace std;

class throttle
{
public:
        throttle();  //default constructor function
        throttle(int size);//other constructor
        throttle(throttle &copy);//copy constructor
        throttle operator+(throttle& temp, throttle& temp2);
        int get_pos(){return position;}
        int get_max(){return max;}
        void shut_off();
        void shift(int amount);
        double flow() const;
        bool is_on() const;

private:
        int position;
        int max;
};

throttle::throttle()
{
max=1;
position=0;
}

throttle::throttle(int size)
{
max=size;
position=0;
}

throttle::throttle(throttle &copy)
{
max=copy.max;
position=copy.position;
}

//operator fxn declaration outside of class


void throttle::shut_off()
{position=0;
}
   
void throttle::shift(int amount)
{
position += amount;
if(position<0)
position=0;
else if (position>max)
position=max;
}

double throttle::flow()const
{
return position/6.0;
}

bool throttle::is_on() const
{
return (flow()>0);
}

int main()
{
throttle total;
throttle sample(10);
sample.shift(5);
throttle sample2(sample);
throttle sample3(sample);
int user_input;

cout << "I have 2 throttles with 10 positions." << endl;
cout << "Where would you like to set the throttle?" << endl;
cout << "Please type a number 0 to 10: ";
cin >> user_input;
sample2.shut_off();
sample2.shift(user_input);

cout << "Second Throttle." << endl;
cout << "Where would you like to set the throttle?" << endl;
cout << "Please type a number 0 to 10: ";
cin >> user_input;
sample3.shut_off();
sample3.shift(user_input);

while (sample2.is_on())
{
cout << "The flow for throttle one is now " << sample2.flow() << endl;
sample2.shift(-1);
}
cout << "The flow is now off" << endl;

while (sample3.is_on())
{
cout << "The flow for throttle two is now " << sample3.flow() << endl;
sample3.shift(-1);
}
cout << "The flow is not off" << endl;

//adding two throttles
return EXIT_SUCCESS;
}

---

operator+(throttle& temp, throttle& temp2); is not a member function.

Code:

---

class throttle {
...
        throttle(throttle&);//copy constructor
        friend        throttle operator+(const throttle& temp,const  throttle& temp2);
...
};
...
throttle operator+(const throttle& temp,const throttle& temp2)
{
        //Your Implementation
}
...
throttle::throttle(throttle & copy)
{
        max=copy.max;
        position=copy.position;
}

---