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C# - Difference between int and int?

In C#, int and int? are two different types of data types. The key difference between them lies in their ability to handle null values. The int is a value type that does not include any null values, while int? is nullable and is shorthand of nullable<int> of value types which can have null value

int:

int is a value type in C# that represents a 32-bit signed integer. It can hold integer values ranging from approximately -2.1 billion to 2.1 billion.

Example: 



int x = 5;

int? (Nullable<int>):

int?, also known as Nullable<int>, is a nullable value type in C#. It allows a value type, such as 'int', to also have a value of null. This is useful when you need to handle situations where a value may not be present or when dealing with databases or APIs that return null values for integer-like fields.

Example: 



int? nullableInt = null;

With int?, you can assign integer values as well as null: 



int? nullableInt = 10;
int? anotherNullableInt = null;

One key distinction is that regular int (value type) cannot be assigned a null value, whereas int? (nullable value type) can be assigned null. For example, by compiling the below code will result in compilation error: 



int x = null; // Compilation error: Cannot convert null to int because it is a non-nullable value type.

In the below example you can see that compiler cannot convert null to int as it is a non-nullable value type and it's showing the compilation error:

difference between int and int? nullable

In contrast, the following code is valid because int? allows for null values: 



int? nullableInt = null; // Valid

Now let's again illustrate this difference with a complete simple C# program: 


using System;

class Program
{
    static void Main()
    {
        int nonNullableInt = 5;
        int? nullableInt = null;

        Console.WriteLine("Non-nullable integer: " + nonNullableInt);
        Console.WriteLine("Nullable integer: " + nullableInt);

        // Trying to assign null to a non-nullable int will cause a compile-time error
        // Uncommenting the following line will result in a compilation error
        // nonNullableInt = null;

        // Assigning a value to nullable int
        nullableInt = 10;
        Console.WriteLine("Nullable integer after assigning value: " + nullableInt);
    }
}

Output of the program: 


Non-nullable integer: 5
Nullable integer: 
Nullable integer after assigning value: 10

In this example:

  • We declare nonNullableInt as an int and assign it the value 5. We cannot assign null to it; doing so would result in a compile-time error.
  • We declare nullableInt as an int? and initially assign it null. Later, we assign it an integer value, demonstrating its ability to hold both null and integer values.

This ability to handle null makes nullable types particularly useful in scenarios like database operations or dealing with external data sources where the presence of a value is not guaranteed.
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