if (dataGridView1.CurrentCell.Value.ToString().Trim() == "Delete" )
{
   dataGridView1.ReadOnly = false;
   dataGridView1.AllowUserToDeleteRows = true;
   string strcon;
   strcon = "Data Source=RAYANEH-C5E4683\\SQLEXPRESS;Initial Catalog=Student;Integrated Security=True";
   SqlConnection con;
   con = new SqlConnection(strcon);
   con.Open();
   String sn;
   SqlCommand cmd = new SqlCommand();
   string sqlDel;
   sn = dataGridView1.CurrentRow.Cells[1].Value.ToString();
   sqlDel = "DELETE FROM stTable WHERE stNo = " + sn;
   cmd.CommandText = sqlDel;
   cmd.Connection = con;
   cmd.ExecuteNonQuery();
   this.student1DataSet.stTable.Clear();
   this.stTableTableAdapter.Fill(this.student1DataSet.stTable);
   dataGridView1.Update();
   con.Close();
   dataGridView1.ReadOnly = true;
}
