C#-Code

public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            nud_StartKm.Maximum = 1000000;
            nud_FinishKm.Maximum = 1000000;
            nud_Cent.Maximum = 1000000;
        }

        //Button zur Berechnung des Erstattungsbetrages
        private void btn_calc_Money_Click(object sender, EventArgs e)
        {           
            //Ermitteln der Differenz des Kilometerstandes
            decimal diff = nud_FinishKm.Value - nud_StartKm.Value;

            //Berechnen der Erstatteten €
            decimal result = diff * (nud_Cent.Value / 100);
            
            lbl_result.Text = "Du bekommst insgesamt " + result.ToString() + "€ erstattet.";
        }

        //Button zur Berechnung der Differenz der Kilometerstände
        private void btn_calc_km_Click(object sender, EventArgs e)
        {
            //Ermitteln der Differenz des Kilometerstandes
            decimal diff = nud_FinishKm.Value - nud_StartKm.Value;

            lbl_result.Text = "Du bist insgesamt " + diff.ToString() + " Kilometer gefahren.";
        }
    }

C#-Code

        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.Label label3;
        private System.Windows.Forms.NumericUpDown nud_StartKm;
        private System.Windows.Forms.NumericUpDown nud_FinishKm;
        private System.Windows.Forms.NumericUpDown nud_Cent;
        private System.Windows.Forms.Label label4;
        private System.Windows.Forms.Button btn_calc_Money;
        private System.Windows.Forms.Button btn_calc_km;
        private System.Windows.Forms.Label lbl_result;

C#-Code

using System.Windows;

/*
        Install NuGet  
        Open your Visual Studio.  
        Open your solution/project.  
        Open Tools menu, select Library Package Manager and select Package Manager Console
        Run the following command "Install-Package Extended.Wpf.Toolkit" 
 */

namespace aufgabe_206
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();           
        }

        struct GUI
        {
            public int km_start;
            public int km_end;
            public int cent_pro_km;
        }

        GUI gui_state = new GUI();

        void update_gui_state()
        {
            gui_state.km_start = (int)this.ud_1.Value;
            gui_state.km_end = (int)this.ud_2.Value;
            gui_state.cent_pro_km = (int)this.ud_3.Value;
        }

        private void ValueChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
        {
            if (!bo_is_loaded)  return;

            update_gui_state();
            string erstattung = ((gui_state.km_end - gui_state.km_start) * gui_state.cent_pro_km * 0.01).ToString("n2") + " €";
            this.textBlock.Text = erstattung;
        }

        bool bo_is_loaded = false;
        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            bo_is_loaded = true;
            button_Click(null, null);
        }

        private void button_Click(object sender, RoutedEventArgs e)
        {
            this.ud_1.Value = this.ud_2.Value;
            update_gui_state();
            ValueChanged(null, null);
        }
    }
}

C#-Code

<Window x:Class="aufgabe_206.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:aufgabe_206"
            xmlns:xctk="http://schemas.xceed.com/wpf/xaml/toolkit"
        mc:Ignorable="d"
        Title="Kilometerrechner mit Erstattungsbetrag" Height="200" Width="725" FontFamily="Courier New" FontWeight="Bold" Background="{DynamicResource {x:Static SystemColors.ActiveCaptionBrushKey}}" BorderThickness="5" BorderBrush="Blue" WindowStartupLocation="CenterScreen" ResizeMode="CanMinimize" Loaded="Window_Loaded">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="60"/>
            <RowDefinition Height="1*"/>
        </Grid.RowDefinitions>
        <StackPanel Margin="10,20,10,0" Orientation="Horizontal">
            
            <Label x:Name="lb_1" Content="km-START" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="10,0,0,0"/>
            <xctk:IntegerUpDown x:Name="ud_1" Width="75" Margin="10,0,0,0" Value="5000" Background="{DynamicResource {x:Static SystemColors.InfoBrushKey}}" ValueChanged="ValueChanged" BorderThickness="5"/>

            <Label x:Name="lb_2" Content="   km-STOP" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="10,0,0,0"/>
            <xctk:IntegerUpDown x:Name="ud_2" Width="75" Margin="10,0,0,0" Value="5000" Background="{DynamicResource {x:Static SystemColors.InfoBrushKey}}" ValueChanged="ValueChanged" BorderThickness="5"/>

            <Label x:Name="lb_3" Content="   CENT/km" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="10,0,0,0"/>
            <xctk:IntegerUpDown x:Name="ud_3" Width="75" Margin="10,0,0,0" Value="39" Background="{DynamicResource {x:Static SystemColors.InfoBrushKey}}" ValueChanged="ValueChanged" BorderThickness="5"/>
            
            <Button x:Name="button" Content=" take END -> START " Margin="10,0,0,0" Click="button_Click"/>

        </StackPanel>
        <TextBlock x:Name="textBlock" Margin="0" Grid.Row="1" TextWrapping="Wrap" FontSize="72" HorizontalAlignment="Center" VerticalAlignment="Center" Foreground="Blue"/>

    </Grid>
</Window>

C#-Code

//  Ist zwar in der Console aber vom Prinzip her das selbe.
// statt Console.WriteLine muss man halt   txt_GefahreneKm.Text = txt_neueKM.Text - txt_alteKM. txt_Erstattung.Text = (txt_neueKM.Text - 
   txt_alteKM)*0.39

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace kmStand
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("AlteKM: ");
            int altKm = Convert.ToInt32(Console.ReadLine());


            Console.WriteLine("NeueKM: ");
            int neueKM = Convert.ToInt32(Console.ReadLine());

            Console.WriteLine("Gefahrene KM: " + (neueKM - altKm));

            Console.WriteLine("Erstattung: " + ((neueKM - altKm) * 0.39) + "Euro");

            Console.ReadKey();
        }
    }
}

C#-Code

namespace _206Kilometerrechner
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnBerechnen_Click(object sender, EventArgs e)
        {
            int differenz = Convert.ToInt32(numUpDownEnde.Value) - Convert.ToInt32(numUpDownAnfang.Value);
            double betrag = Convert.ToDouble(tbCent.Text) * differenz;
            MessageBox.Show("Gefahrene Kilometer: " + differenz + " Km\nErstattungbetrag: " + betrag + " €", "Ergebnis", MessageBoxButtons.OK);
        }
    }
}

C#-Code

 private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label label2;
        private System.Windows.Forms.Label label3;
        private System.Windows.Forms.NumericUpDown numUpDownAnfang;
        private System.Windows.Forms.NumericUpDown numUpDownEnde;
        private System.Windows.Forms.TextBox tbCent;
        private System.Windows.Forms.Button btnBerechnen;