Correctly Check and Use Nullable Variables in C#

C# handles null checks differently for value types (like int) versus reference types (like string). After checking for null with the `is` operator, value types require accessing the `.Value` property to use the underlying value, while reference types can be used directly. This is because nullable value types use the `Nullable<T>` wrapper class with `.HasValue` and `.Value` properties, whereas reference types natively support null values without special wrappers.