как переделать функцию в классе, чтоб значение передавалось по ссылке

// Testpoint.cpp
//
 
 
#include "Point.hpp"
//#include "Linesegment.hpp"
 
#include <string>
#include <iostream>
#include <string>
#include <sstream>
 
using namespace std;
 
Point::Point() : x(0), y(0) // Colon syntax!!!!!!!!!!!!!!!!!
{// Default constructor
//  x = y =0.0;
}
 
Point::Point(double newx, double newy) : x(newx), y(newy)
{// Initialize using newx and newy
    
//  x = newx;
//  y = newy;
}
Point::~Point()
{// Des...
    
    cout << "bye my point..\n";
}
 
double Point::getX() const
{
    return x;
}
 
void Point::setX(double newX)
{ 
    x = newX;
}
 
 
double Point::getY()  const
{
    return y;
}
 
void Point::setY(double newY)
{ 
    y = newY;
} 
 
 
void print(const Point& pt)
{
    cout << "(" << pt.getX() << "," << pt.getY() << ")" << endl;    
}
 
 
double Point::ToString (double x, double y)
{
    ostringstream os;
    os << "Point (" << x << ", " << y << ")";
    cout << os.str() << '\n';
    return x,y;
}
 
 
double DistanceOrigin(double x, double y)
{
    double DistanceO;
    DistanceO = sqrt (x*x + y*y);
    return DistanceO;
}
 
 
    double Distance(double x1, double y1, double x2, double y2)
    {
    double Distance, Distance_sqr;
 
    Distance_sqr = x1*x1-2*x2*x1+x2*x2 + y1*y1-2*y2*y1+y2*y2; 
     
    Distance = sqrt(Distance_sqr);
    return Distance;
 
    }
 
 
 
    
int main()
 
{
    double a1, b1,a2,b2;
    cout << "Please enter point coordinates x and y of point 1  :\n";
    cin >> a1 >> b1; // input x and y coordinates value by user
 
 
    cout << "Please enter point coordinates x and y of point 2  :\n";
    cin >> a2 >> b2; // input x and y coordinates value by user
 
    // Create a point
 
    Point p1 (0,0); // creating object with inicial coordinates
    Point p2 (0,0);
    print(p1); // print for checking 
    print(p2);
 
    p1.setX(a1); // setting the point coordinates x into user value 
    p1.setY(b1); // setting the point coordinates y into user value 
 
    p2.setX(a2); // setting the point coordinates x into user value 
    p2.setY(b2); // setting the point coordinates y into user value 
    
 
    
    cout << "(" << p1.getX() << "," << p1.getY() << ")" << endl;
    cout << "(" << p2.getX() << "," << p2.getY() << ")" << endl;
    
 
    print(p1); // printing the point coordinates using print() function
 
    p1.ToString(p1.getX(),p1.getY()); // printing the point coordinates using ToString() function
    p2.ToString(p2.getX(),p2.getY());
 
    cout <<" Printing the point coordinates using the get functions of point1: " << p1.getX() <<" , "<< p1.getY()<<" " << endl;
 
    cout <<" Printing the point coordinates using the get functions of point2: " << p2.getX() <<" , "<< p2.getY()<<" " << endl;
 
    
    cout << "distanceO: " << DistanceOrigin(p1.getX(),p1.getY());
    cout << endl;
    cout << "distance between two points: " << Distance(p1.getX(),p1.getY(),p2.getX(),p2.getY()); 
    // а просто 2 точки
    cout << endl;
    system ("pause");
    return 0;
 
    
 
}