A constructor is similar to a method however it doesn't have any return value, moreover we use the public keyword before its definition.

    using System;

    class Program
    {
        struct Point
        {
            public double x;
            public double y;
    
            public Point(double x, double y)
            {
                this.x = x;
                this.y = y;
            } 
        }
    
        struct Triangle
        {
            public Point[] vertices;
    
            public Triangle(Point a, Point b, Point c)
            {
                this.vertices = new Point[] { a, b, c };
            }
    
            // Calculates and returns the area of the triangle based on the vertices.
            public double getArea()
            {
                // Storing the values in shorter variables for ease of use and code readability.
                double x1 = this.vertices[0].x;
                double x2 = this.vertices[1].x;
                double x3 = this.vertices[2].x;
    
                double y1 = this.vertices[0].y;
                double y2 = this.vertices[1].y;
                double y3 = this.vertices[2].y;
    
                // Calculating and returning the area of the triangle. 
                // This formula is easy available on the internet, you don't need to understand it.
                return (0.5) * ( x1 * (y2 - y3) + x2 * (y3 - y1) + x3 * (y1 - y2) );
            }
        }
            
        static void Main(string[] args)
        {
            Point p1 = new Point(47, 17);
            Point p2 = new Point(9, 50);
            Point p3 = new Point(7, 14);
    
            Triangle tri = new Triangle(p1, p2, p3);
    
            Console.WriteLine(tri.getArea());
        }
    }