2D Array

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WPFArrays
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Random rand = new Random();
        List<Serie> lstSerie = new List<Serie>();
        List<Rectangle> _rect = new List<Rectangle>();
        int b = 0;


        public MainWindow()
        {

            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            txtRes.Clear();
            Serie objSerie = new Serie();
            b = b + 1;
            objSerie.B = b;
            int[,] getallen = new int[rand.Next(1,10), rand.Next(1,5)];
            for (int i = 0; i < getallen.GetLength(0); i++)
            {
                for (int j = 0; j < getallen.GetLength(1); j++)
                {
                    getallen[i, j] = rand.Next(30);
                }
            }
            objSerie.Nummers = getallen;
            lstSeries.Items.Add(objSerie);
            for (int i = 0; i < getallen.GetLength(0); i++)
            {
                for (int j = 0; j < getallen.GetLength(1); j++)
                {
                    string data = String.Format("{0}\t", getallen[i, j]);
                    txtRes.AppendText(data);
                }
                txtRes.AppendText(Environment.NewLine);
            }
        }
        private void lstSeries_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            cnvTekening.Children.Clear();
            _rect.Clear();
            txtRes.Clear();
            Serie objSerie = (Serie)lstSeries.SelectedItem;
            for (int i = 0; i < objSerie.Nummers.GetLength(0); i++)
            {
                for (int j = 0; j < objSerie.Nummers.GetLength(1); j++)
                {
                    string data = String.Format("{0}\t", objSerie.Nummers[i, j]);
                    txtRes.AppendText(data);
                }
                txtRes.AppendText(Environment.NewLine);
            }
            int Lengte = 420 / objSerie.Nummers.GetLength(1);
            double   Lengte2 = 0;
            double Breedte = 238 / objSerie.Nummers.GetLength(1);
            for (int z = 0; z < objSerie.Nummers.GetLength(1); z++)
            {
                Rectangle rect = new Rectangle();
                rect.Height = Lengte;
                rect.Width = objSerie.Nummers[0,z]*7;
                rect.Stroke = new SolidColorBrush(Colors.Blue);
                rect.StrokeThickness = 1;
                Canvas.SetTop(rect,Lengte2);
                _rect.Add(rect);
                Lengte2 += Lengte;
            }
            foreach (var rect in _rect)
            {
                cnvTekening.Children.Add(rect);
            }
        }

        private void btnSum_Click(object sender, RoutedEventArgs e)
        {
            int a = 0;
            Serie objSerie = (Serie)lstSeries.SelectedItem;
            foreach (int nummer in objSerie.Nummers)
            {
                a += nummer;
            }
            MessageBox.Show(String.Format("Het totaal van alle nummers is {0}",a),"SUM");
        }

        private void btnAvg_Click(object sender, RoutedEventArgs e)
        {
            int a = 0;
            int c = 0;
            Serie objSerie = (Serie)lstSeries.SelectedItem;
            foreach (int nummer in objSerie.Nummers)
            {
                a += nummer;
                c++;
            }
            a = a / c;
            MessageBox.Show(String.Format("Het gemiddelde van alle nummers is {0}", a), "Gemiddelde");
        }

        private void btnMin_Click(object sender, RoutedEventArgs e)
        {
            Serie objSerie = (Serie)lstSeries.SelectedItem;

            int a = 1000;
            foreach (int nummer in objSerie.Nummers)
            {
                if ( a > nummer)
                {
                    a = nummer;
                }
            }
            MessageBox.Show(String.Format("Het laagste getal is {0}", a), "Minimum");
        }

        private void btnMax_Click(object sender, RoutedEventArgs e)
        {
            Serie objSerie = (Serie)lstSeries.SelectedItem;

            int a = 0;
            foreach (int nummer in objSerie.Nummers)
            {
                if ( a < nummer)
                {
                    a = nummer;
                }
            }
            MessageBox.Show(String.Format("Het hoogste getal is {0}", a), "Maximum");

        }
    }
}