How to edit gridview in asp.net

public partial class _Default : System.Web.UI.Page
{
    SqlConnection cn = new SqlConnection("Data Source=.\\sqlexpress;Initial Catalog=test;integrated security=true;");
    SqlDataAdapter adp;
    DataSet ds = new DataSet();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            ViewState["exp"] = "name";
            datab();
        }
    }
    private void datab()
    {
        adp = new SqlDataAdapter("select * from emp order by " + ViewState["exp"].ToString(), cn);
        adp.Fill(ds, "first");
        GridView1.DataSource = ds;
        GridView1.DataBind();

    }
    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;
        datab();
    }
    protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        GridView1.EditIndex = -1;
        datab();
    }
    protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        string str;
        str = GridView1.DataKeys[e.RowIndex].Value.ToString();

        cn.Open();
        SqlCommand cmd = new SqlCommand("delete from emp where name=@name", cn);
        cmd.Parameters.AddWithValue("@name", str);
        cmd.ExecuteNonQuery();
        cn.Close();

        GridView1.EditIndex = -1;
        datab();
    }
    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        string str;
        str = GridView1.DataKeys[e.RowIndex].Value.ToString();

        cn.Open();
        SqlCommand cmd = new SqlCommand("update emp set name=@name,age=@age,city=@city where name=@org_name", cn);
        TextBox t1, t2, t3;
        t1 =(TextBox) GridView1.Rows[e.RowIndex].FindControl("TextBox1");
        t2 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextBox2");
        t3 = (TextBox)GridView1.Rows[e.RowIndex].FindControl("TextBox3");  

        cmd.Parameters.AddWithValue("@name", t1.Text );
        cmd.Parameters.AddWithValue("@age", t2.Text );
        cmd.Parameters.AddWithValue("@city", t3.Text );
        cmd.Parameters.AddWithValue("@org_name", str);
        cmd.ExecuteNonQuery();
        cn.Close();

        GridView1.EditIndex = -1;
        datab();
    }
    protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        GridView1.PageIndex = e.NewPageIndex;
        GridView1.EditIndex = -1;
        datab();
    }
    protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
    {
        ViewState["exp"] = e.SortExpression.ToString();
        GridView1.EditIndex = -1;
        datab();
    }
}