Cannot implicitly convert type 'void' to 'string'

Question

BAL.cs

public void Delete(string id)
      {
          cmd = new MySqlCommand("DeleteProduct", con);
          cmd.CommandType = CommandType.StoredProcedure;
          cmd.Parameters.AddWithValue("in_ProductId", id);
          con.Open();
          int i = cmd.ExecuteNonQuery();
          con.Close();
      }

Home Controller

public ActionResult DeleteProduct(string id)
       {

           try
           {
               BAL objBAL = new BAL();
               string product = objBAL.Delete(id); //error
               if (product != null)
               {
                 Response.Write("<script>alert('Data Deleted Successfully')</script>");
               }

           }
           catch (Exception ex)
           {
               throw ex;
           }
       }