Extension methods for built-in types in C Sharp (C#) - Mini Project: Build & Apply

Extension Methods for Built-in Types

📖 Scenario: Imagine you want to add a new helpful action to a built-in type in C#. For example, you want to add a way to check if a number is even or odd directly on the number itself.

🎯 Goal: You will create an extension method for the built-in int type that checks if a number is even. Then you will use this method to print whether some numbers are even or not.

📋 What You'll Learn

Create a static class called IntExtensions

Inside it, create a public static method called IsEven that extends int

The IsEven method returns true if the number is even, otherwise false

Use the IsEven method on some numbers and print the results

💡 Why This Matters

🌍 Real World

Extension methods let you add new features to existing types without changing their code. This is useful when working with built-in types or libraries you cannot modify.

💼 Career

Knowing how to write extension methods is important for C# developers to write clean, reusable, and readable code that extends functionality in a natural way.

1

Create a static class for extension methods

Create a public static class called IntExtensions to hold extension methods.

C Sharp (C#)

// Your code here

Need a hint?

Extension methods must be inside a static class.

2

Add an extension method IsEven for int

Inside the IntExtensions class, create a public static method called IsEven that extends int using this int number as the first parameter. The method should return true if number % 2 == 0, otherwise false.

C Sharp (C#)

public static class IntExtensions
{
    // Your code here
}

Need a hint?

Use the this keyword before the first parameter to make it an extension method.

3

Use the IsEven extension method on some numbers

In the Main method, create an int variable called num and set it to 4. Then use num.IsEven() to check if it is even and store the result in a bool variable called result.

C Sharp (C#)

public static class IntExtensions
{
    public static bool IsEven(this int number)
    {
        return number % 2 == 0;
    }
}

class Program
{
    static void Main()
    {
        // Your code here
    }
}

Need a hint?

Call the extension method like a normal method on the variable.

4

Print the result of the IsEven check

Add a Console.WriteLine statement to print "4 is even: " followed by the value of result.

C Sharp (C#)

public static class IntExtensions
{
    public static bool IsEven(this int number)
    {
        return number % 2 == 0;
    }
}

class Program
{
    static void Main()
    {
        int num = 4;
        bool result = num.IsEven();
        // Your code here
    }
}

Need a hint?

Use string interpolation with $ and curly braces to include variables in the output.