Working with nulls on value type structures

Int32, bool, float, etc. are all memory structures, and the value of "null" is a pointer (a zero pointer precisely) therefore it isn't possible to assign null to an attribute. This in itself isn't an issue until you throw in a database. The values from the database can be null, but what strategies exist for working with null values in memory from one of the value types? I'm using C# to build a system. Thanks in advance.