# 3.6: Types

In this module we'll talk about Value Types, DateTimeOffset, and Reference Types.

## Value Types Review

* `DateTimeOffset` is a **value** type, they *can't be null*.
* Adding the ? to `ModifiedUtc` allows a value type to be null.
* It's good to store dates with `DateTimeOffset`, this way it will account for time zones.
* We will format the date & time in [Part 11.](https://eleven-fifty-academy.gitbook.io/dotnet-201-elevennote/elevennote-parts-1-11/part-11-dateformat/11.0-dateformat)

### Important:

* Let's say it again: Notice the `?` after the `DateTimeOffset` for the `ModifiedUtc`. This allows the value type to be null. The `?` is referred to as the null-conditional operator. Just making sure you caught that!

## Reference Types

Just for the sake of review let's note something important:

* Objects are **reference** types, they *can be null*.
* Reference Types point to an address in memory.

Just a little review.