Connections SQL Server 2008 R2 (open and close)

Hi there i hope someone can help me with this issue.

From another part of the program I want to call a class so I can:

1. Open a SQL Connection
2. Do many queries
3. Close a SQL Connection

The reason to leave the Connection open is because I want to save workload in the server.

I have the following code which is not working with CloseCnn().

Also Im not sure if conn should be a public var so the value doesnt change until I close the Connection.

Thank you for the help

Code:

---

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace PixelCheckSum.Controllers
{
    class BDController
    {
        public SqlConnection conn;
        public static void OpenCnn()
        {
            // 1. Instantiate the connection
            SqlConnection conn = new SqlConnection("Data Source=(local);Initial Catalog=Northwind;Integrated Security=SSPI");
            try
            {
                // 2. Open the connection
                if (conn.State == ConnectionState.Open)
                {
                    conn.Close();
                }
                conn.Open();
               
            }
            catch(Exception ex)
            {
                MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }

        public static void CloseCnn()
        {
            try
            {
                //Close the connection
                if (conn != null)
                {
                    conn.Close();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }
}

---

What errors are you getting? And exactly what is it that isn't working?