private void button_AddCar_Click(object sender, EventArgs e)
        {
            try
            {
                Car_Inventory car = new Car_Inventory();

                AssignCar(ref car);

                string str = car.Year.ToString() + " " + car.Make + " with" + " miles.";
                listBox_Display.Items.Add(str);
            }
            catch
            {
                MessageBox.Show("Provide wrong input");
                comboBox_Make.Text   = "";
                comboBox_Year.Text   = "";
                comboBox_Milage.Text = "";

                comboBox_Make.Focus();
            }
        }
 private void AssignCar(ref Car_Inventory car)
 {
     car.Make    = comboBox_Make.SelectedItem.ToString();
     car.Year    = int.Parse(comboBox_Year.SelectedItem.ToString());
     car.Mileage = int.Parse(comboBox_Milage.Text);
 }