Custom LINQ extension methods in C Sharp (C#) - Mini Project: Build & Apply

Custom LINQ Extension Methods

📖 Scenario: You work with lists of numbers and want to create your own special filters and operations, just like LINQ does. This helps you reuse code and write cleaner programs.

🎯 Goal: Build a custom LINQ extension method called IsEven that filters only even numbers from a list of integers.

📋 What You'll Learn

Create a list of integers called numbers with the values 1, 2, 3, 4, 5, 6

Create a boolean extension method called IsEven for integers

Use the IsEven method in a LINQ Where clause to filter even numbers

Print the filtered even numbers separated by spaces

💡 Why This Matters

🌍 Real World

Custom LINQ extension methods help you add your own reusable filters and operations to collections, making your code cleaner and easier to read.

💼 Career

Many software jobs require writing clean, reusable code. Knowing how to create and use extension methods is a valuable skill for working with collections and LINQ in C#.

1

Create the list of numbers

Create a list of integers called numbers with these exact values: 1, 2, 3, 4, 5, 6.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // Create the list called numbers with values 1, 2, 3, 4, 5, 6
        // Your code here
    }
}

Need a hint?

Use List<int> and initialize it with the values inside curly braces.

2

Create the IsEven extension method

Create a public static class called Extensions. Inside it, create a public static method called IsEven that takes this int number as a parameter and returns true if the number is even, otherwise false.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List numbers = new List { 1, 2, 3, 4, 5, 6 };
    }
}

// Create the Extensions class and IsEven method below
// Your code here

Need a hint?

Extension methods must be inside a static class and have this before the first parameter.

3

Use IsEven in a LINQ Where clause

Inside Main, create a variable called evenNumbers that uses numbers.Where(n => n.IsEven()) to filter only even numbers.

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List numbers = new List { 1, 2, 3, 4, 5, 6 };
        // Create evenNumbers using numbers.Where and IsEven
        // Your code here
    }
}

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

Need a hint?

Use Where with a lambda expression calling IsEven() on each number.

4

Print the filtered even numbers

Print the evenNumbers separated by spaces using Console.WriteLine(string.Join(" ", evenNumbers)).

C Sharp (C#)

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        List numbers = new List { 1, 2, 3, 4, 5, 6 };
        var evenNumbers = numbers.Where(n => n.IsEven());
        // Print the evenNumbers separated by spaces
        // Your code here
    }
}

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

Need a hint?

Use Console.WriteLine with string.Join to print the numbers separated by spaces.