Line / Segment classes

#include <iostream>
#include <math.h>

using namespace std;

class Grid {
    public:
        bool parallel(Grid& line) {
            return line.slope == slope;
        }
        float slope;
};

class Segment: public Grid {
    public:
        Segment(float _x1 = 0, float _y1 = 0, float _x2 = 0, float _y2 = 0) {
            x1 = _x1;
            x2 = _x2;
            y1 = _y1;
            y2 = _y2;
            slope = (_y2 - _y1) / (_x2 - _x1);
            length = sqrt(pow(_x2 - _x1, 2) + pow(_y2 - _y1, 2));
        }
        float length, x1, x2, y1, y2;
};

class Line: public Grid {
    public:
        Line(float _slope) {
            slope = _slope;
        }
};

int main() {
    Line l_one(5);
    Line l_two(5);
    cout << l_one.parallel(l_two) << endl;  /* true, they have the same slope */

    Segment s_one(1, 2, 50, 100);
    Segment s_two(-50, -100, 0, 0);
    cout << s_one.parallel(s_two) << endl;  /* true, they also have the same slope */
}