Nullable Types in C#

In C#, nullable types are a feature introduced to allow value types (such as int, double, bool, etc.) to have a value of null, in addition to their normal range of values. This is particularly useful in scenarios where you need to represent the absence of a value or where a value might legitimately be undefined.

• 1. Declaration and assignment

  You can declare and assign a value to a data type (double, char, int, bool) or you can also declare and assign a null value to vairable in C# 2.0.

Example

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double? pi = 3.14;
char? letter = 'a';
int m2 = 10;
int? m = m2;
bool? flag = null;
// An array of a nullable value type:
int?[] arr = new int?[10];
double? pi = 3.14;
char? letter = 'a';
int m2 = 10;
int? m = m2;
bool? flag = null;
// An array of a nullable value type:
int?[] arr = new int?[10];
• 2. Check Nullable Value Type

  You can use is operator to check both a vairable of datatype is nullable or not and retireveing a value of an mentioned type.

Example

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int? a = 42;

if (a is int valueOfA)

{

Console.WriteLine($"a = {valueOfA}");

}

else

{

Console.WriteLine("a does not have a value");

}

// Output:

// a = 42

int? a = 42;

if (a is int valueOfA)

{

Console.WriteLine($"a = {valueOfA}");

}

else

{

Console.WriteLine("a does not have a value");

}

// Output:

// a = 42

• 3. Check Nullable Type With HasValue Property:

  You can check a vairable of mentioned data type has null value or not with HasValue property.

Example

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int? b = 10;
if (b.HasValue)
{
Console.WriteLine($"b = {b.Value}");
}
else
{
Console.WriteLine("b does not have a value");
}
// Output:
// b = 10
int? b = 10;
if (b.HasValue)
{
Console.WriteLine($"b = {b.Value}");
}
else
{
Console.WriteLine("b does not have a value");
}
// Output:
// b = 10
• 4. Check Nullable Type With null:

  You can also check a variable of a nullable value type with null instead using the HasValue property.

Example

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int? c = 7;
if (c != null)
{
Console.WriteLine($"c = {c.Value}");
}
else
{
Console.WriteLine("c does not have a value");
}
// Output:
// c = 7
int? c = 7;
if (c != null)
{
Console.WriteLine($"c = {c.Value}");
}
else
{
Console.WriteLine("c does not have a value");
}
// Output:
// c = 7
• 5. Null Coalescing Operator:

  You can use Coalescing Operator to check either value is null or not if it is null then assign a value.

Example

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int? a = 28;
int b = a ?? -1;
Console.WriteLine($"b = {b}");    // output: b = 28
int? c = null;
int d = c ?? -1;
Console.WriteLine($"d = {d}");    // output: d = -1
int? a = 28;
int b = a ?? -1;
Console.WriteLine($"b = {b}");    // output: b = 28
int? c = null;
int d = c ?? -1;
Console.WriteLine($"d = {d}");    // output: d = -1
• 6. Lifted operators:

  The predefined unary and binary operators or any overloaded operators that are supported by a value type T are also supported by the corresponding nullable value type T?

Example

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int? a = 10;
int? b = null;
int? c = 10;
a++;       // a = 11
a = a * c;     // a = 110
a = a + b;      // a = null
int? a = 10;
int? b = null;
int? c = 10;
a++;       // a = 11
a = a * c;     // a = 110
a = a + b;      // a = null
• 7. Boxing and unboxing:

  An instance of a nullable value type T? is boxed as follows:

Example

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int a = 41;
object aBoxed = a;
int? aNullable = (int?)aBoxed;
Console.WriteLine($"Value of aNullable: {aNullable}");
object aNullableBoxed = aNullable;
if (aNullableBoxed is int valueOfA)
{
Console.WriteLine($"aNullableBoxed boxed: {valueOfA}");
}
// Output:
// Value of aNullable: 41
// aNullableBoxed boxed: 41
int a = 41;
object aBoxed = a;
int? aNullable = (int?)aBoxed;
Console.WriteLine($"Value of aNullable: {aNullable}");
object aNullableBoxed = aNullable;
if (aNullableBoxed is int valueOfA)
{
Console.WriteLine($"aNullableBoxed boxed: {valueOfA}");
}
// Output:
// Value of aNullable: 41
// aNullableBoxed boxed: 41
• 8. identify a nullable value type:

  The is operator is used to check whether an object is compatible with a given type. It returns true if the object is of the specified type or can be cast to that type; otherwise, it returns false.

Example

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object fruitName = "Apricot";
if (obj is string)
{
Console.WriteLine("A Fruit Apricot.");
}
object fruitName = "Apricot";
if (obj is string)
{
Console.WriteLine("A Fruit Apricot.");
}

Summary

Nullable types in C# provide a straightforward way to handle scenarios where values might be absent or undefined without resorting to less expressive workarounds. They are widely used in various applications, particularly in database interactions and scenarios where optionality of values is necessary.