Hi Kannnan I think this is this the best for u

http://www.c-sharpcorner.com/UploadFile/raj1979/GridViewExample11232008075052AM/GridViewExample.aspx

  To get edit mode in c# .net datagridview write the following code.

     protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;
        bindgrid();
    }

void bindgrid()
    {
        cn = new SqlConnection(ConfigurationManager.ConnectionStrings[1].ConnectionString);
        cn.Open();
        SqlCommand cmd = new SqlCommand("select * from stud", cn); // stud is a table name.
        SqlDataReader dr = cmd.ExecuteReader();
        GridView1.DataSource = dr;
        GridView1.DataBind();
    }