public double ZKilometer(Fahrten[] data)
        {
            double z = 0;

            foreach (Fahrten f in data)
            {
                z += f.kilometer;
            }

            return z;
        }
        public DataTable Fahrtenbuch(Fahrten[] data)
        {
            // Initiiere Tabelle
            DataTable table = new DataTable();

            DataColumn column;

            column = table.Columns.Add();
            column.ColumnName = "Von";
            column.DataType = typeof(string);

            column = table.Columns.Add();
            column.ColumnName = "Bis";
            column.DataType = typeof(string);

            column = table.Columns.Add();
            column.ColumnName = "Kilometer";
            column.DataType = typeof(double);

            DataRow row;

            foreach (Fahrten f in data)
            {
                row = table.NewRow();

                row["Von"] = String.Format("{0:d/M/yyyy HH:mm}", f.Von);
                row["Bis"] = String.Format("{0:d/M/yyyy HH:mm}", f.Bis);
                row["Kilometer"] = f.kilometer;
                table.Rows.Add(row);
            }

            return table;
        }