private void btnDodadiAvtomobil_Click(object sender, EventArgs e)
        {
            if (cbMarki.SelectedIndex == -1)
            {
                string message = "Изберете марка!";
                string caption = "Неуспешно додавање на автомобил";
                MessageBox.Show(message, caption, MessageBoxButtons.OK, MessageBoxIcon.Error);
                return;
            }

            if (txtModel.Text.Trim().Length == 0)
            {
                string message = "Внесете модел!";
                string caption = "Неуспешно додавање на автомобил";
                MessageBox.Show(message, caption, MessageBoxButtons.OK, MessageBoxIcon.Error);
                return;
            }

            Avtomobil avtomobil = new Avtomobil();

            avtomobil.Marka = cbMarki.SelectedItem as Marka;
            avtomobil.Model = txtModel.Text;
            avtomobil.Cena = nupCena.Value;
            avtomobil.Potrosuvacka = nupPotrosuvacka.Value;

            lstAvtomobili.Items.Add(avtomobil);
            ClearValues();
            RefreshComputation();
        }
        private void RefreshComputation()
        {
            decimal averageConsumption = 0M;
            decimal minConsumption = Decimal.MaxValue;
            decimal maxPrice = Decimal.MinValue;
            Avtomobil minCar = null;
            Avtomobil maxCar = null;

            foreach (Avtomobil item in lstAvtomobili.Items)
            {
                if (item.Cena > maxPrice)
                {
                    maxPrice = item.Cena;
                    maxCar = item;
                }

                if (item.Potrosuvacka < minConsumption)
                {
                    minConsumption = item.Potrosuvacka;
                    minCar = item;
                }

                averageConsumption += item.Potrosuvacka;
            }

            if ((minCar != null && maxCar != null) || averageConsumption != 0M)
            {
                txtNajskap.Text = maxCar.ToString();
                txtNajekonomicen.Text = minCar.ToString();
                txtProsecnaPotrosuvacka.Text = (averageConsumption / lstAvtomobili.Items.Count).ToString("0.0");
            }
            else
            {
                ClearComputed();
            }
        }