Adding numbers - Rhea

#include <GL/gl.h>
#include <GLUT/glut.h>
//#include <GL/glui.h>
 
using namespace std;
 
#define RED 0
#define GREEN 1
#define BLUE 2
#define PI 3.14159
 
class Surface;
class BouncingLine;
 
Surface * surface;
BouncingLine * bl;
 
int height = 480, width = 640;
 
struct VelocityVector {
 
	float dx, dy;
 
	VelocityVector() { ; }
	VelocityVector(float dx, float dy) {
		this->dx = dx;
		this->dy = dy;		
	}
 
	void flipX() {
		this->dx *= -1;
	}
 
	void flipY() {
		this->dy *= -1;
	}
 
	string toString() {
        stringstream ss;
        ss << '(' << setprecision(2) << this->dx << ',' << setprecision(2) << this->dy << ')';
        return ss.str();
    }
 
    friend ostream& operator<< ( ostream& stream, VelocityVector& vv) {
        stream << vv.toString();
        return stream;
    }
 
};