Database：

 public static class dbconnection{

         static string cons = "data source = (local) ;initial catalog = RentManage;integrated security = true;";

         static SqlConnection con = null;

         public static SqlCommand dbconn(string sql, params SqlParameter[] pms)

         {/*连接方法*/

             try{

                 con = new SqlConnection(cons);con.Open();

                 SqlCommand cmd = new SqlCommand(sql, con);

                 if (pms != null){ cmd.Parameters.AddRange(pms); }

                 return cmd;

             }catch {return null; }

         }

         public static int ExecuteNonQuery(string sql, params SqlParameter[] pms)

         {//与执行相关

             SqlCommand cmd = dbconn(sql, pms);

             if (cmd != null){

                 try{ return cmd.ExecuteNonQuery(); }

 catch{ return -;//-1错误码是未查到结果

                 }finally{ if (con != null) con.Close(); }

             }return -;

         }

         public static object ExecuteScalar(string sql, params SqlParameter[] pms)

         {/*登录*/

             object obj = -;//-2错误码是未连接成功

             SqlCommand cmd = dbconn(sql, pms);

             if (cmd != null){

                 try{ obj = cmd.ExecuteScalar();

                 }catch{ obj = -;//-1错误码是未查到结果

                 }finally{ if (con != null) con.Close(); }

             }return obj;

         }

         public static DataTable ExecuteDataTable(string sql, params SqlParameter[] pms)

         { //把查询到的数据填充到表格里

             try{

                 con = new SqlConnection(cons);

                 SqlCommand cmd = new SqlCommand(sql, con);

                 SqlDataAdapter adapter = new SqlDataAdapter(cmd);

                 if (pms != null){

                     adapter.SelectCommand.Parameters.AddRange(pms);

                 }

                 DataSet dataset = new DataSet();

                 adapter.Fill(dataset);

                 return dataset.Tables[];

             }catch (Exception exp){ throw exp;

             }finally{ if (con != null) con.Close(); }

         }

         public static SqlDataReader ExecuteReader(string sql, params SqlParameter[] pms)

         {//读取查询的信息

             SqlCommand cmd = dbconn(sql, pms);

             if (cmd != null){

                 try{

                     return cmd.ExecuteReader(CommandBehavior.CloseConnection);

                 }catch (Exception exp){

                     if (con != null){ con.Close();  }

                     throw exp;

                 }

             }return null;

         }