winforms update help??

Question

hi all i have created a datagridview to display my records from db,and now i want to update the records below shown is my code

 
SqlDataAdapter da = new SqlDataAdapter("select * from emp", con);
SqlCommandBuilder cb = new SqlCommandBuilder(da);
DataSet ds = new DataSet();
dataGridView1.DataSource = ds.Tables[0];
da.UpdateCommand = cb.GetUpdateCommand();
da.Update(ds);

but when i execute the code and update the values they are not getting updated in my database??i dnt know y?? plz help me with this,thanks.