二维向量类

class Vector2d
{
public:
	Vector2d():x(0.0),y(0.0){};

	Vector2d(double _x,double _y) :x(_x),y(_y){}

	Vector2d(const Vector2d& _vect2d)
	{
		x = _vect2d.x;
		y = _vect2d.y;
	}

	double dotProduct(const Vector2d& vec2d) const
	{
		return vec2d.x*x + vec2d.y*y;
	}

	void normal()
	{
		double dLen = length();
		x = x / dLen;
		y = y / dLen;
	}

	double length() const { return sqrt(x*x+y*y);}

	double angle()
	{

	}

	Vector2d rotateBy(double dAngle) const    //角度旋转公式推导（使用三角变换来推导）
	{
		return Vector2d(x*cos(dAngle)-y*sin(dAngle),x*sin(dAngle)+y*cos(dAngle));
	}

	Vector2d& negate()    //向量求反
	{
		return Vector2d(-x,-y);
	}

	Vector2d  operator * (double dScl) const
	{
		return Vector2d(dScl*x,dScl*y);
	}    

	Vector2d operator + (const Vector2d & vec)
	{
		return Vector2d(x+vec.x, y+vec.y);
	}

	Vector2d& operator += (const Vector2d& vec)
	{
		x = x + vec.x;
		y = y + vec.y;
		return *this;
	}

	Vector2d operator - (const Vector2d& vec)
	{
		return Vector2d(x-vec.x,y-vec.y);
	}
	Vector2d& operator -= (const Vector2d& vec)
	{
		x = x-vec.x;
		y = y-vec.y;
		return *this;
	}

public:
	double x,y;
};