Pasted

using System;
using System.Collections.Generic;
using System.Linq;
 
namespace Flächenberechnung {
  struct Vektor2D {
    public int X { get; set; }
    public int Y { get; set; }
 
    public Vektor2D(int x, int y) {
      this.X = x;
      this.Y = y;
    }
  }
 
  class Program {
    static void Main(string[] args) {
      IEnumerable<Vektor2D> points = new Vektor2D[] {
        // 1. Rechteck
        new Vektor2D(0, 0), new Vektor2D(5, 0), new Vektor2D(0, 5), new Vektor2D(5, 5),
        
        // 2. Rechteck
        new Vektor2D(5, 3), new Vektor2D(5,5),new Vektor2D(7,3), new Vektor2D(7,5)
      };
 
      points = points.OrderBy(v => v.Y).ThenBy(v => v.X).Distinct().ToList();
 
      Func<Vektor2D, Vektor2D, double> Determinante = (Vektor2D v1, Vektor2D v2) => Math.Abs(v1.X * v2.Y - v1.Y * v2.X);
 
      var fläche = 0.0;
      Vektor2D vek = new Vektor2D();
      foreach (var p in points) {
        if (vek.X != 0 || vek.Y != 0) {
          fläche += Determinante(vek, p) / 2;
        }
        vek = p;
      }
 
      Console.WriteLine($"Die Fläche beträgt: {fläche}");
      Console.ReadLine();
    }
  }
}