I have been trying to understand solution code of this problem given by Isanchez_Aguilar. I am having trouble in understanding function inline Vector operator+ & — both. I am also not able to get what "Vector():x(0), y(0) {}" &"Vector(Double _x, Double _y):x(_x), y(_y) {}" are supposed to mean.

Isanchez_Aguilar's solution code is below and you can also use this link:https://github.com/isanchez-aguilar/UVa-Solutions/blob/master/10242%20-%20Fourth%20Point%20!!.cpp

<spoiler summary="/* * User: Isanchez_Aguilar * Problem: UVA 10242 — Fourth Point !! */

include <bits/stdc++.h>

using namespace std;

typedef double Double;

const Double EPS = 1e-3;

inline Double isEqual(Double a, Double b) { return fabs(a — b) < EPS; }

class Vector { public: Double x; Double y;

Vector():x(0), y(0) {}

Vector(Double _x, Double _y):x(_x), y(_y) {}

inline bool operator==(const Vector& a) const { return isEqual(x, a.x) and isEqual(y, a.y); }

inline Vector operator+(const Vector& a)
{
    Vector b;
    b.x = x + a.x;
    b.y = y + a.y;

    return b;
}

inline Vector operator-(const Vector& a)
{
    Vector b;
    b.x = x - a.x;
    b.y = y - a.y;

    return b;
}

};

Vector points[4];

int main(void) { ios_base::sync_with_stdio(0); cin.tie(0);

cout.precision(3);
cout.setf(ios::fixed);

while (cin >> points[0].x >> points[0].y)
{
    for (int i = 1; i < 4; ++i)
       cin >> points[i].x >> points[i].y;

    int a = 1;
    int b = 0;
    int c = 2;

    if (points[0] == points[2])
    {
       a = 0;
       b = 1;
       c = 3;
    }
    else if (points[0] == points[3])
    {
       a = 0;
       b = 1;
       c = 2;

    }
    else if (points[1] == points[2])
       c = 3;

    Vector p = points[c] + points[b] - points[a];

    cout << p.x << " " << p.y << "\n";
}

return 0;

}"> ...