Help mates with E-commerce website ASP.NET C# page.cs line 32

using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Web.UI.WebControls;

public partial class Shopping_website_user_product_desc : System.Web.UI.Page
{
    private string connectionString = ConfigurationManager.ConnectionStrings["shoppingmaster"].ConnectionString;
    private int id;
    private int qty;
    private string product_name, product_desc, product_images;


    protected Label l1;
    protected Label l2;
    protected Button b1;
    protected Label t1;
    protected Label lblPrice;
    protected TextBox txtQuantity;

    protected void Page_Load(object sender, EventArgs e)
    {
        if (Request.QueryString["id"] == null)
        {
            Response.Redirect("display_item.aspx");
        }
        else
        {
            id = Convert.ToInt32(Request.QueryString["id"]);

            if (!IsPostBack)
            {
                using (SqlConnection con = new SqlConnection(connectionString))
                {
                    con.Open();
                    SqlCommand cmd = con.CreateCommand();
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = "SELECT * FROM product WHERE id = @id";
                    cmd.Parameters.AddWithValue("@id", id);

                    SqlDataReader reader = cmd.ExecuteReader();

                    if (reader.Read())
                    {
                        product_name = reader["product_name"].ToString();
                        product_desc = reader["product_desc"].ToString();
                        product_images = reader["product_images"].ToString();
                    }

                    reader.Close();

                    DataTable dt = new DataTable();
                    SqlDataAdapter da = new SqlDataAdapter(cmd);
                    da.Fill(dt);

                    d1.DataSource = dt;
                    d1.DataBind();

                    con.Close();
                }
            }
           
        


        qty = get_qty(id);

                    if (qty == 0)
                    {
                        l2.Visible = false;
                        txtQuantity.Visible = false;
                        b1.Visible = false;
                        l1.Text = "There is no available quantity of this item.";
                    }
                    // Loop through the items in the Repeater
                    foreach (RepeaterItem item in d1.Items)
                    {
                        TextBox txtQuantity = (TextBox)item.FindControl("t1");
                        if (txtQuantity != null)
                        {
                            if (IsPostBack)
                            {
                                int product_qty = Convert.ToInt32(txtQuantity.Text);
                                txtQuantity.Text = product_qty.ToString();
                            }
                            else
                            {
                                txtQuantity.Text = "1"; // Set a default value if needed
                            }
                        }
                    }
                }
        }
    

    protected void btnMinus_Click(object sender, EventArgs e)
    {
        Button btnMinus = (Button)sender;
        RepeaterItem item = (RepeaterItem)btnMinus.NamingContainer;
        TextBox t1 = (TextBox)item.FindControl("t1");

        int product_qty = Convert.ToInt32(t1.Text);
        if (product_qty > 1)
        {
            product_qty--;
            t1.Text = product_qty.ToString();
        }
    }
    protected void btnPlus_Click(object sender, EventArgs e)
    {
        Button btnPlus = (Button)sender;
        RepeaterItem item = (RepeaterItem)btnPlus.NamingContainer;
        TextBox t1 = (TextBox)item.FindControl("t1");

        int product_qty = Convert.ToInt32(t1.Text);
        product_qty++;
        t1.Text = product_qty.ToString();
    }
    private bool UserLoggedIn()
    {
        // Check if the user is logged in
        // Return true if logged in, false otherwise

        // For example, you can check if a user session exists:
        return Session["user"] != null;
    }

    protected void b1_Click(object sender, EventArgs e)
    {
        if (!UserLoggedIn())
        {
            // User is not logged in, redirect to the login page
            Response.Redirect("login.aspx?returnUrl=product_desc.aspx?id=" + id);
            return;
        }

        using (SqlConnection con = new SqlConnection(connectionString))
        {
            con.Open();
            RepeaterItem item = (RepeaterItem)((Button)sender).NamingContainer;
            TextBox t1 = (TextBox)item.FindControl("t1");

            if (t1 != null && !string.IsNullOrEmpty(t1.Text))
            {
                int product_qty;
                if (int.TryParse(t1.Text, out product_qty))
                {
                    double product_price = GetProductPrice(id);

                    if (product_price == 0)
                    {
                        // Product price not found, handle the error
                        lblPrice.Text = "Error: Product price not found.";
                        return;
                    }

                    double totalPrice = product_price * product_qty;
                    double taxAmount = totalPrice * 0.15;
                    totalPrice += taxAmount;

                    if (lblPrice != null)
                    {
                        lblPrice.Text = "Total Price (including 15% tax): " + totalPrice.ToString("C2");
                    }

                    SqlCommand cmd = con.CreateCommand();
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = "SELECT * FROM registration WHERE email=@email";
                    cmd.Parameters.AddWithValue("@email", Session["user"]);
                    SqlDataReader dr = cmd.ExecuteReader();

                    if (dr.Read())
                    {
                        string firstname = dr["firstname"].ToString();
                        string lastname = dr["lastname"].ToString();
                        string email = dr["email"].ToString();
                        string address = dr["address"].ToString();
                        string city = dr["city"].ToString();
                        string state = dr["state"].ToString();
                        string pincode = dr["pincode"].ToString();
                        string mobile = dr["mobile"].ToString();
                        string product_name = this.product_name; // Assign the product name from the class variable
                        string product_images = this.product_images; // Assign the product images from the class variable

                        if (!string.IsNullOrEmpty(product_name) && !string.IsNullOrEmpty(product_images))
                        {
                            SqlCommand cmd3 = con.CreateCommand();
                            cmd3.CommandType = CommandType.Text;
                            cmd3.CommandText = "INSERT INTO orders (firstname, lastname, email, address, city, state, pincode, mobile, DateOfOrder, payment_status, product_id, product_name, product_price, product_qty, total_price, product_images) " +
                                              "VALUES (@firstname, @lastname, @email, @address, @city, @state, @pincode, @mobile, @DateOfOrder, @payment_status, @product_id, @product_name, @product_price, @product_qty, @total_price, @product_images)";

                            cmd3.Parameters.AddWithValue("@firstname", firstname);
                            cmd3.Parameters.AddWithValue("@lastname", lastname);
                            cmd3.Parameters.AddWithValue("@email", email);
                            cmd3.Parameters.AddWithValue("@address", address);
                            cmd3.Parameters.AddWithValue("@city", city);
                            cmd3.Parameters.AddWithValue("@state", state);
                            cmd3.Parameters.AddWithValue("@pincode", pincode);
                            cmd3.Parameters.AddWithValue("@mobile", mobile);
                            cmd3.Parameters.AddWithValue("@DateOfOrder", DateTime.Now);
                            cmd3.Parameters.AddWithValue("@payment_status", "Pending");
                            cmd3.Parameters.AddWithValue("@product_id", id);
                            cmd3.Parameters.AddWithValue("@product_name", product_name);
                            cmd3.Parameters.AddWithValue("@product_price", product_price);
                            cmd3.Parameters.AddWithValue("@product_qty", product_qty);
                            cmd3.Parameters.AddWithValue("@total_price", totalPrice);
                            cmd3.Parameters.AddWithValue("@product_images", product_images);
                            cmd3.ExecuteNonQuery();
                        }

                        else
                        {
                            dr.Close();
                        }

                        // ...

                        // Update the product quantity
                        SqlCommand cmd1 = con.CreateCommand();
                        cmd1.CommandType = CommandType.Text;
                        cmd1.CommandText = "UPDATE product SET product_qty = product_qty - @quantity WHERE id = @id";
                        cmd1.Parameters.AddWithValue("@quantity", product_qty);
                        cmd1.Parameters.AddWithValue("@id", id);
                        cmd1.ExecuteNonQuery();

                        // Retrieve the last inserted order ID
                        int orderId = GetLastInsertedOrderId();

                        // Add the item to the cookie
                        if (Request.Cookies["aa"] == null)
                        {
                            Response.Cookies["aa"].Value = product_name + "," + product_desc + "," + product_price + "," + product_qty + "," + product_images + "," + id + "," + orderId;
                            Response.Cookies["aa"].Expires = DateTime.Now.AddDays(1);
                        }
                        else
                        {
                            Response.Cookies["aa"].Value = Request.Cookies["aa"].Value + "|" + product_name + "," + product_desc + "," + product_price + "," + product_qty + "," + product_images + "," + id + "," + orderId;
                            Response.Cookies["aa"].Expires = DateTime.Now.AddDays(1);
                        }
                    }
                }
            }
        }
    }

            public int get_qty(int id)
        {
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                con.Open();

                SqlCommand cmd = con.CreateCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "SELECT product_qty FROM product WHERE id=@id";
                cmd.Parameters.AddWithValue("@id", id);
                SqlDataReader dr = cmd.ExecuteReader();

                if (dr.Read())
                {
                    qty = Convert.ToInt32(dr["product_qty"]);
                }

                dr.Close();
            }

            return qty;
        }

        public int GetLastInsertedOrderId()
        {
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                con.Open();

                SqlCommand cmd = con.CreateCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "SELECT TOP 1 Id FROM orders ORDER BY Id DESC";
                int orderId = Convert.ToInt32(cmd.ExecuteScalar());

                return orderId;
            }
        }

        public double GetProductPrice(int id)
        {
            using (SqlConnection con = new SqlConnection(connectionString))
            {
                con.Open();

                SqlCommand cmd = con.CreateCommand();
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = "SELECT product_price FROM product WHERE id=@id";
                cmd.Parameters.AddWithValue("@id", id);
                object result = cmd.ExecuteScalar();

                if (result != null && double.TryParse(result.ToString(), out double price))
                {
                    return price;
                }

                return 0;
            }
        }
 }