C# Functional Programming Tutorial – Complete Guide

Welcome to this comprehensive tutorial where we delve into the world of C# functional programming. If coding games or building robust software systems is your linear programming cup of tea, this tutorial will spark your curiosity further into the functional programming paradigm of the C# language. The beauty of C# functional programming lies in its simplicity, maintainability, and testability that allow novice and experienced coders like you to create more efficient and robust code. In this tutorial, we will walk you through this unique paradigm, providing you with a solid foundation to upgrade your C# coding skills.

What is C# Functional Programming?

In its simplest form, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids changing-state and mutable data. This notion, when applied to C#, allows us to create more concise, predictable, and easier-to-test code.

Why Learn C# Functional Programming?

C# is a versatile language widely used in game development, notably with Unity, and in a range of software development applications. Incorporating functional programming practices into your C# knowledge base will allow you to:

  • Write cleaner and more concise code: With functional programming, you can accomplish more with fewer lines of code, enhancing readability and maintainability.
  • Improve testability: Functions in functional programming are easier to test because of their predictability – the same input will always produce the same output.
  • Boost productivity: Functional programming concepts such as immutability and statelessness can significantly reduce bugs and debugging time, ultimately boosting your productivity.

Being adept in C# functional programming can therefore be a great addition to your coding arsenal whether you are a beginner just embarking on your coding journey or an experienced developer.

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Getting Started with Functional Programming in C#

The foundation of functional programming in C# starts with understanding functions as first-class entities. This allows us to use functions as arguments, return them from other functions, or assign them to variables. We can see an example of this below:

Func addFive = x => x + 5; 
Console.WriteLine(addFive(10)); // Outputs 15

This approach gives us the freedom to operate with functions, opening possibilities for higher-level functions.

Lambda Expressions and Anonymous Functions in C#

C# functional paradigm widely uses lambda expressions. Lambda expressions are anonymous functions that you can use to create delegates or expression tree types. They can be used to define simple functions inline.

Func square = x => x * x;
Console.WriteLine(square(5)); // Outputs 25

We can also use lambda expressions to filter, map and reduce collections in a functional manner. Here is an example:

List numbers = new List {1, 2, 3, 4, 5};

IEnumerable squareNumbers = numbers.Select(x => x * x); 
Console.WriteLine(string.Join(", ", squareNumbers)); // Outputs 1, 4, 9, 16, 25

Immutable Data in Functional Programming

In functional programming, data is usually immutable. This means that instead of changing data, we create new data. This idea can be counter-intuitive but it has some strong advantages like thread safety and predictability.

public class ImmutableCircle
    public ImmutableCircle(double radius)
        Radius = radius;

    public double Radius { get; }

    public ImmutableCircle With(double radius)
        return new ImmutableCircle(radius);

As we can see in this example, an ImmutableCircle can’t change its radius after being created. We provide a method to create a new circle with a different radius.

Functional Composition

Functional composition is a fundamental concept in functional programming. It is the process of combining two or more functions to produce a new function. Here is how we can do it in C#:

Func addFive = x => x + 5;
Func doubleIt = x => x * 2;
Func addFiveAndDouble = x => doubleIt(addFive(x));
Console.WriteLine(addFiveAndDouble(5)); // Outputs 20

In this code, we compose the two functions, addFive and doubleIt, to form a new function, addFiveAndDouble.

Pure Functions in C#

Pure functions are another critical component of functional programming. A function is considered “pure” if it always produces the same output for the same input and does not produce any side effects. Below is an example of a pure function.

public static int Add(int a, int b)
    return a + b;
Console.WriteLine(Add(5, 4)); // Outputs 9

Higher-Order Functions

Functional programming in C# also involves the use of higher-order functions. A higher-order function is a function that takes one or more functions as arguments, returns a function, or both. Below is an example:

Func Multiplier(int factor)
    return x => x * factor; 

var doubleIt = Multiplier(2);
Console.WriteLine(doubleIt(5)); // Outputs 10

In this example, Multiplier is a higher-order function as it returns another function.

Map, Filter, and Reduce

Map, Filter, and Reduce operations are common in functional programming, allowing us to perform common list operations in a functional way.

An example of the Map operation in action:

List numbers = new List {1, 2, 3, 4, 5};
IEnumerable squareNumbers = numbers.Select(x => x * x);
Console.WriteLine(string.Join(", ", squareNumbers)); // Outputs 1, 4, 9, 16, 25

Filter operation showcased:

IEnumerable evenNumbers = numbers.Where(x => x % 2 == 0);
Console.WriteLine(string.Join(", ", evenNumbers)); // Outputs 2, 4

Reduce (or Aggregate in C#) operation example:

int product = numbers.Aggregate(1, (x, y) => x * y);
Console.WriteLine(product); // Outputs 120

The Map, Filter, and Reduce operations provide a powerful toolkit for processing data without mutating state, aligning perfectly with the principles of functional programming.


The power and elegance of C# functional programming lie in its simplicity, its capability of dealing with state change, and potential for clean and concise code. This approach opens up a world of possibilities for designing more efficient software with fewer bugs. By fostering a mental discipline of coding, functional programming makes your software more modular, more maintainable, and more comprehensible.

At Zenva, we believe in continually growing and innovating in the field of programming education. Learning to code needs not be daunting; with the right guidance and training, anyone can become proficient. Learn and perfect C# functional programming with us and take your programming skills to the next level!

Exploring More Features in C# Functional Programming

As we navigate the extensive realm of functional programming in C#, let’s dive deeper into more examples showcasing vital principles and techniques that define this popular paradigm.

Action T Delegate

A handy feature is the Action<T> delegate, representing a method that returns void and takes a single parameter. Below is an example:

Action print = message => Console.WriteLine(message);
print("Hello, Zenva!"); // Outputs: Hello, Zenva!

In this example, we’ve declared an Action<T> delegate to encapsulate any method that takes a single string parameter and returns void.

Func T Delegate

Another useful C# delegate when coding functionally is Func<T, TResult>. This delegate type represents a method that accepts an argument of type T and returns a TResult. Have a look at a simple example:

Func intToString = x => x.ToString();
Console.WriteLine(intToString(123)); // Outputs: 123

In this example, we’ve declared a Func<T, TResult> delegate represents a method that accepts an integer and returns its string representation.


The concept of delegates in C# is fundamental to functional programming. Delegates stand for a reference to a method. In simpler terms, they point to functions.

public delegate int MathOperation(int a, int b);
public static int Sum(int a, int b) => a + b;

MathOperation operation = Sum;
Console.WriteLine(operation(5, 7)); // Outputs: 12

In this scenario, we declared a delegate MathOperation and a static method Sum. Later, we used a delegate instance operation to reference the Sum method and call it.

LINQ in Functional Programming

The Language Integrated Query (LINQ) in C# adds powerful querying capabilities to .NET languages, allowing you to interact with objects, databases, and XML in a more functionally-oriented way. Let’s see this in action:

List numbers = new List{1,2,3,4,5,6,7,8,9};

// Using LINQ's powerful querying capabilities
var query = from number in numbers
            where number % 2 == 0
            select number;

foreach (int num in query)
    Console.Write(num + " ");  // Outputs: 2 4 6 8

In the example above, we are using some key LINQ expressions to filter out even numbers from a given list.


Currying is another powerful concept borrowed from mathematics, which involves breaking down a function that takes multiple arguments into a series of functions that take a single argument. Let’s demonstrate this with an example:

// Non-curried method
Func add = (x, y) => x + y;
Console.WriteLine(add(5, 3)); // Outputs: 8

// Curried method
Func<int, Func> curriedAdd = x => y => x + y;
Console.WriteLine(curriedAdd(5)(3)); // Outputs: 8

The beauty of currying is that it allows you to create new functions on-the-fly by partially applying some arguments to your function.

As you’ve seen, C# functional programming opens a world of possibilities, making your code concise, readable, and maintainable. Incorporating these principles into your daily coding practice will no doubt elevate your skills to a whole new level.

The Next Steps in Your Journey

Now that you have a better grasp of the C# functional programming principles and concepts, you may be wondering where to go next? Well, the world of coding is vast and full of exciting opportunities, and at Zenva, we’re here to guide you every step of the way.

We recommend checking out our comprehensive Unity Game Development Mini-Degree. This mini-degree is a collection of 20 courses designed to teach game development using Unity, one of the most popular game engines globally. Not only does Unity have extensive usage in the gaming industry, but it’s also widely used in non-game industries like architecture, film, and education. The mini-degree caters to beginners just setting off on their game development journey and more experienced learners looking to upskill.

Moreover, check out our broad range of over 250 supported courses, from beginner to professional, in programming, game development, and AI through our Unity collection. Learning with us allows you to explore various dimensions of coding, game creation, and more at your convenience, opening new exciting doors in your career pursuits.

Welcome aboard and enjoy your coding journey with us at Zenva!


In this comprehensive overview of C# functional programming, we’ve navigated through its fundamental concepts, principles, and examples, taking your understanding of C# to new heights. The techniques discussed provide a valuable toolkit for creating more efficient, cleaner, and maintainable code, crucial for your progression as a versatile coder comfortable in various realms of programming.

At Zenva, we’re passionate about empowering learners like you with the skills to create and innovate. Our expansive course catalogue, including our best-selling Unity Game Development Mini-Degree, provides hands-on, high-quality content to escalate your learning journey. Are you ready to embrace the captivating world of coding and game creation? Join us, and let’s write a world-changing code together!

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