Grid view update operation error occurs

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C#

i am doing update using grid view.when i update error occurs as follows;

my code as follows;

protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        string Sno = ((TextBox)GridView1.Rows[e.RowIndex]
                            .FindControl("txtSno")).Text;
        string Name = ((TextBox)GridView1.Rows[e.RowIndex]
                            .FindControl("txtName")).Text;
        string Age = ((TextBox)GridView1.Rows[e.RowIndex]
                            .FindControl("txtage")).Text;
        string Address = ((TextBox)GridView1.Rows[e.RowIndex].FindControl("txtaddress")).Text;

        SqlConnection con = new SqlConnection("Server=(local);initial catalog=master;Trusted_Connection=True");
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "update Details set Sno=@Sno, Name=@Name," +
     "Age=@Age where Sno=@Sno;" +
     "select Sno,Name,Age,Address from Details";
        cmd.Parameters.Add("@Sno", SqlDbType.Int).Value = Sno;
        cmd.Parameters.Add("@Name", SqlDbType.VarChar).Value = Name;
        cmd.Parameters.Add("@Age", SqlDbType.VarChar).Value = Age;
        cmd.Parameters.Add("@Address", SqlDbType.VarChar).Value = Address;
        cmd.ExecuteNonQuery();
        SqlCommand cmd1 = new SqlCommand("Select * from Details", con);
        SqlDataAdapter adp = new SqlDataAdapter(cmd1);
        DataSet ds = new DataSet();
        adp.Fill(ds);
        GridView1.DataSource = ds;
        GridView1.DataBind();
        GridView1.EditIndex = -1;
        cmd.Connection = con;
        con.Close();
    }

the error occurs as follows, ExecuteNonQuery: Connection property has not been initialized. ( cmd.ExecuteNonQuery();) in this line error occurs please help me.what is my problem in the above code.