Point a = ...;
Point b = ...;
double d = ...;
a = a + b;
a = a - b;
a += b;
a -= b;
a = d*b;
a = b*d;
a *= d;
std::cout << a << std::endl;

#ifndef NBODY_SIM_POINT_H
#define NBODY_SIM_POINT_H

#include <iostream>

struct Point {
  // coordinates
  double x;
  double y;

public:
    Point();
    Point(double x_p, double y_p);

    Point operator+(const Point& b);
    Point operator-(const Point& b);

    Point& operator*=(double d);
    Point& operator+=(const Point& b);
    Point& operator-=(const Point& b);

    friend Point operator*(const double& d, const Point& b);
    friend Point operator*(const Point& b, const double& d);

    friend std::ostream& operator<<(std::ostream& os, const Point& a);
};

#endif //NBODY_SIM_POINT_H