The document discusses nullable types in C#. Nullable types allow value types to be assigned null values by using the Nullable<T> structure. Some key points are: nullable types can only be used with value types, not reference types; the Value property returns the value if not null, HasValue returns true if a value is assigned; comparison uses == != operators or the Nullable static class; nullable types are useful for representing null/undefined values in databases or as alternatives to reference types. An example shows assigning an integer nullable type a value and accessing its value.

2. NULLABLE TYPE IN C#
Presented by
MUHAMMAD ZOHAIB ANWER
FA17-BCS-105

3. Definition:
The Nullable type allows you to assign a null value to a
variable. Nullable types can only work with Value Type not
with Reference Type because it already contains a null value.
In C#, the compiler does not allow you to assign a null value to
a variable. So, C# 2.0 provides a special feature to assign a null
value to a variable that is known as the Nullable type.

4. EXPLANATION:
NULL literally means nothing - a variable that doesn't yet hold
a value. A nullable type can represent the correct range of
values for its underlying value type, plus an
additional null value. For example, Nullable<int> can be
assigned any value from -2147483648 to 2147483647, or a
null value. A nullable type has the same assignment rules as a
value type.
It must be assigned a value before using it if nullable types are
declared in a function as local variables. If it is a field of any
class then it will have a null value by default.

5. Characteristics of Nullable Types:
Nullable types can only be used with value types.
The Value property will throw an InvalidOperationException if value is
null; otherwise it will return the value.
The HasValue property returns true if the variable contains a value, or false
if it is null.
You can only use == and != operators with a nullable type. For other
comparison use the Nullable static class.
Nested nullable types are not allowed. Nullable<Nullable<int>> i; will give
a compile time error.

6. Advantage of Nullable Types:
The main use of nullable type is in database applications. Suppose,
in a table a column required null values, then you can use nullable
type to enter null values.
Nullable type is also useful to represent undefined value.
You can also use Nullable type instead of reference type to store a
null value.

7. IMPORTANT POINTS TO REMEMBER
• Nullable<T> type allows assignment of null to value types.
• ? operator is a shorthand syntax for Nullable types.
• Use value property to get the value of nullable type.
• Use HasValue property to check whether value is assigned to nullable
type or not.
• Static Nullable class is a helper class to compare nullable types.

8. CODE EXAMPLE

9. PROGRAM IS IN RUNNING STATE(OUTPUT)

10. IF I ASSIGN ANY VALUE TO NULLABLE
VARIABLE

11. RESULT WILL BE:

12. using System;
namespace ConsoleApp4
{
class Program
{
static void Main(string[] args)
{
//ASSIGNING ANY VALUE RATHER THAN NULL
int? TicketOnSale = 100;
int AvailableTicket;
if (TicketOnSale == null)
{
AvailableTicket = 0;
}
else
{
AvailableTicket = (int)TicketOnSale;
}
Console.WriteLine("AvailableTicket:{0}", AvailableTicket);
}
}
}