repl.it - Irregular Polygon Area

#include <iostream>
#include <vector>
using namespace std;

class Point {
public:
    Point(double xX, double yY)
    : x{xX}, y{yY} {
        // empty validation body //
    }

    double x{0.0};
    double y{0.0};

};

class Polygon {
public:
    int qty{0};

    void addPoint(Point p) {
        int item{0};

        cin >> qty;
        for (int i = 1; i <= qty; i += 1) {
            cin >> item;
            points.push_back(item);
        }// push point p into the vector
    }

    Point getPoint(int index) {
        // return the point from the vector at location index
    }

    size_t size() const {
        return points.size(); // return the number of points in the vector
    }

    double area() {
        for (int i{1}; i < points.size(); i += 1) {

        }


    } // calculate the area by iterating over the points

private:
    vector<Point> points{};

};

int main()
{
    Polygon a{}; // define a polygon variable
    a.addPoint(); // put points into the polygon
    a.area(); // call the area function

    return 0;
}