>>>Is it OK or not really a good code
>>>
>>>

>>>string strOrderNo = this.txtOrderNo.Text;
>>>                        int? OrderNo;
>>>                        if (strOrderNo.Equals(String.Empty))
>>>                            OrderNo = null;
>>>                        else
>>>                            OrderNo = Convert.ToInt32(strOrderNo);
>>>
>>>                        _dtOrder = biz.Find(OrderNo, this.dtgStartDate.Value, this.dtgEndDate.Value);

>>>
>>
>>That should be fine. I'd probably do something like this, but it's mostly a style preference:
>>
>>

>>int? orderNo = null;
>>if (!string.IsNullOrEmpty(strOrderNo))
>>   orderNo = Convert.ToInt32(strOrderNo);
>>
>>dtOrder = biz.Find(orderNo, this.dtgStartDate.Value, this.dtgEndDate.Value);
>>

>Or just

dtOrder = biz.Find((orderNo == String.Empty) ?  (int?) null :  Convert.ToInt32(orderNo), this.dtgStartDate.Value, this.dtgEndDate.Value);

But null converts to zero so you'd probably need:

int? i2 = (orderNo == String.Empty) ?  (int?) null : (orderNo==null)? (int?)null : Convert.ToInt32(orderNo);

which gets a little less readable. In practice probably better to use TryParse() anyway.....
Best,
Viv