[source lang=cpp]struct vector2f{    float x,y;    vector2f(float x_, float y_) : x(x_), y(y_) {}    void normalize()    {        float len = sqrt(x*x + y*y);        x /= len;        y /= len;    }	vector2f vabs()	{		vector2f temp(0,0);		temp.x = abs(x);		temp.y = abs(y);		return temp;	}    vector2f operator-(vector2f const& other)    {        return vector2f(x - other.x, y - other.y);    }	vector2f operator+(vector2f const& other)	{		return vector2f(x + other.x, y + other.y);	}	vector2f operator*(vector2f const& other)	{		return vector2f(x * other.x, y * other.y);	}		int operator>(vector2f const& other)	{		if(x >= other.x && y >= other.y) return 1;		else return 0;	}	int operator<(vector2f const& other)	{		if(x < other.x && y < other.y) return 1;		else return 0;	}	};void Update_Bullets(){	vector2f temp(0,0);	ib = bullets.begin();	id = dirs.begin();	idest = dests.begin();	while((ib != bullets.end() && id != dirs.end()) && idest != dests.end())	{		//move bullets according to dir and speed		*ib = *ib + (*id * speed);		// compensate for changes in viewpoint		if(old_world_x < world_x) ib->x-= TILE_SIZE * (world_x - old_world_x); 		if(old_world_x > world_x) ib->x+= TILE_SIZE * (old_world_x - world_x);		if(old_world_y < world_y) ib->y-= TILE_SIZE * (world_y - old_world_y); 		if(old_world_y > world_y) ib->y+= TILE_SIZE * (old_world_y - world_y);				temp = *ib - *idest;		temp = temp.vabs();		//erase offscreen bullets		if((ib->x <= 0 || ib->x >= SCREEN_W) || (ib->y <= 0 || ib->y >= SCREEN_H) || (temp < thresh))		{			bullets.erase(ib);			dirs.erase(id);			dests.erase(idest);		}		else		{			ib++;			id++;			idest++;		}	}	//reset veiw checking values	old_world_x = world_x;	old_world_y = world_y;}