How To Cast The Value In C# Resulted From Max() Command In SQL Server Developer

Could anyone help of how to cast the value in C# resulted from max() command. To complicate the matter, from the query result I see in the Microsoft SQL Server Management Studio, if there are records the value is number. But if there are no records, the value is NULL. How do I handle these two possible different conditions?

I have tried:

- string test = (string)reader["MaxOrderID"];

- int test = Convert.ToInt32((string)reader["MaxOrderID"]);

- string test = Convert.ToInt32(reader["MaxOrderID"]).ToString();

all failed. And what do I do if the value is NULL. And also how do I do to cope with these two different possible conditions? 

For example, I have the following code:command.CommandText = "Select max(OrderID) as 'MaxOrderID' from [Order]";command.CommandType = CommandType.Text;

 

command.Connection = conn;

command.Connection.Open();

reader = command.ExecuteReader();

reader.Read();

??? orderID = ???reader["MaxOrderID"];