Combobox'daki parçanın fiyatını değişkene toplama

using System;
using System.Data.SQLite;

class Program
{
    static void Main()
    {
        string connectionString = "Data Source=mydatabase.db;Version=3;";
        string query = "SELECT * FROM TableName";

        using (SQLiteConnection connection = new SQLiteConnection(connectionString))
        {
            connection.Open();

            using (SQLiteCommand command = new SQLiteCommand(query, connection))
            {
                using (SQLiteDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        // Veri okuma işlemleri burada gerçekleştirilir
                        // Örneğin: reader.GetString(0), reader.GetInt32(1), vb.
                    }
                }
            }

            connection.Close();
        }
    }
}

using System;
using System.Data.SqlClient;

class Program
{
    static void Main()
    {
        string connectionString = "Data Source=myServerAddress;Initial Catalog=myDatabase;User ID=myUsername;Password=myPassword;";
        string query = "SELECT * FROM TableName";

        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            using (SqlCommand command = new SqlCommand(query, connection))
            {
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        // Veri okuma işlemleri burada gerçekleştirilir
                        // Örneğin: reader.GetString(0), reader.GetInt32(1), vb.
                    }
                }
            }

            connection.Close();
        }
    }
}

private void button2_Click_1(object sender, EventArgs e)
{
 if (modelbox.SelectedItem != null)
 {
 PartItem partItem = (PartItem)modelbox.SelectedItem;
 listBox1.Items.Add(partItem.Name + " - " + partItem.Price.ToString("N2", new CultureInfo("tr-TR")) + " TL");
 totalCost += partItem.Price;
 label5.Text = "Toplam Fiyat: " + totalCost.ToString("N2", new CultureInfo("tr-TR")) + " TL";
 }
}

while (dr.Read())
{
    modelbox.Items.Add(dr["mad"].ToString());//ALAN ADI
}

PartItem(partID, partName, partPrice)

public class PartItem
{
    public int ID { get; set; }
    public string Name { get; set; }
    public double Price { get; set; }

    public PartItem(int id, string name, double price)
    {
        ID = id;
        Name = name;
        Price = price;
    }

    public override string ToString()
    {
        return Name;
    }
}