how to update datatable into sql table using c#

Question

DataRow dr = dt.Rows.Find(new object[] { custm_id });

if (dr == null)

{

// dt.Rows.Add(dr);

dr = dt.NewRow();

val=true;

dr["custmid"] = custm_id;

}

else

{

dr.BeginEdit();

}

 

dr["fieldname"] = "test";

if (val)

{

dt.Rows.Add(dr);

}

else

{

dr.EndEdit();

}

 

like this i have edited table.

changes affected in datatable  

 

SqlDataAdapter adapter;

using (adapter = new SqlDataAdapter("SELECT  fieldname FROM customlist", con))

 using (new SqlCommandBuilder(adapter))

{

 

 adapter.Update(dt);

} 

  when i try to update

its updatating only new row.  not updating edited rows into sql table.

how is possible any one help