Need it this way...

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            bindgrid();
        }
    }

    public void bindgrid()
    {
        SqlConnection con = new SqlConnection("Data Source=STD-258E51EA446\\SQLEXPRESS;Initial Catalog=Employee;Integrated Security=True");
        SqlCommand cmd = new SqlCommand("Select * from emp", con);
        con.Open();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        cmd.ExecuteScalar();
        GridView1.DataSource = ds;
        GridView1.DataBind();
        con.Close();
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("Data Source=STD-258E51EA446\\SQLEXPRESS;Initial Catalog=Employee;Integrated Security=True");
        SqlCommand cmd = new SqlCommand("insert into emp(name,desg,sal,city,email) values('" + TextBox1.Text + "','" + TextBox2.Text + "', '" + TextBox3.Text + "', '" + TextBox4.Text + "','" + TextBox5.Text + "')", con);
        con.Open();
        cmd.ExecuteNonQuery();
        bindgrid();
        con.Close();
    }
    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;
        bindgrid();

    }
    protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        GridView1.EditIndex = -1;
        bindgrid();
    }
    protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        GridView1.PageIndex = e.NewPageIndex;
        bindgrid();
    }
    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {

      }