Topic 11812 min readStructured Tutorial

C# Lambda Expressions - Practical Examples Tutorial

Quick Answer

Lambda expressions in C# provide a concise way to represent anonymous methods using syntax similar to mathematical functions. They are widely used for inline code, especially with LINQ queries and delegates, enabling more readable and maintainable code.

Learning Objectives

Explain the purpose of Practical Examples in a practical learning context.
Identify the main ideas, terms, and decisions involved in Practical Examples.
Apply Practical Examples in a simple real-world scenario or practice task.

Introduction to C# Lambda Expressions

Lambda expressions are a powerful feature in C# that allow you to write inline anonymous functions. They simplify code by reducing boilerplate and improving readability.

This tutorial focuses on practical examples to help you understand how to use lambda expressions effectively in real-world scenarios.

Lambda expressions enable concise and expressive code.

Understanding Lambda Expression Syntax

A lambda expression uses the syntax: parameters => expression or parameters => { statements }. It can be assigned to delegates or used directly in LINQ queries.

The left side specifies input parameters, and the right side contains the expression or block of code to execute.

Single parameter without parentheses: x => x * x
Multiple parameters with parentheses: (x, y) => x + y
Expression body: x => x > 5
Statement body: x => { Console.WriteLine(x); return x > 5; }

Practical Examples of Lambda Expressions

Let's explore common scenarios where lambda expressions simplify your C# code.

Using Lambda with Delegates

Delegates represent references to methods. Lambda expressions provide a concise way to define delegate instances inline.

Define a delegate for a method that takes an int and returns bool.
Assign a lambda expression to the delegate.
Invoke the delegate to execute the lambda.

Filtering Collections with LINQ and Lambda

Lambda expressions are commonly used with LINQ to filter, transform, and query collections efficiently.

Use Where() method with a lambda to filter items.
Use Select() method with a lambda to project items.
Combine multiple LINQ methods with lambdas for complex queries.

Event Handling with Lambda Expressions

Lambdas provide a neat way to define event handlers inline without separate methods.

Subscribe to events using lambda expressions.
Write concise event handler logic directly in the subscription.

Practical Example

This example defines a delegate using Func<int, bool> and assigns a lambda that checks if a number is even.

This example filters a list to include only even numbers using the Where method with a lambda expression.

This example shows how to subscribe to a button click event using a lambda expression as the event handler.

Examples

Lambda with Delegate Example

Func<int, bool> isEven = x => x % 2 == 0;
Console.WriteLine(isEven(4)); // Output: True

This example defines a delegate using Func<int, bool> and assigns a lambda that checks if a number is even.

Filtering a List with LINQ and Lambda

var numbers = new List<int> {1, 2, 3, 4, 5};
var evenNumbers = numbers.Where(n => n % 2 == 0).ToList();
Console.WriteLine(string.Join(", ", evenNumbers)); // Output: 2, 4

This example filters a list to include only even numbers using the Where method with a lambda expression.

Event Subscription Using Lambda

button.Click += (sender, e) => { Console.WriteLine("Button clicked!"); };

This example shows how to subscribe to a button click event using a lambda expression as the event handler.

Best Practices

Use lambdas for short, simple operations to improve readability.
Avoid overly complex lambdas; extract logic into named methods if needed.
Use explicit parameter types in lambdas when clarity is important.
Leverage lambdas with LINQ for clean and expressive data queries.

Common Mistakes

Writing very long or complex lambdas that reduce code clarity.
Ignoring delegate type compatibility leading to compilation errors.
Overusing lambdas where named methods would be more maintainable.
Forgetting to handle exceptions inside lambda expressions.

Hands-on Exercise

Create a Lambda to Square Numbers

Write a lambda expression that takes an integer and returns its square. Use it to transform a list of numbers.

Expected output: A list of squared numbers printed to the console.

Hint: Use Func<int, int> delegate and LINQ Select method.

Filter Strings Starting with 'A'

Use a lambda expression with LINQ to filter a list of strings, returning only those that start with the letter 'A'.

Expected output: A list of strings starting with 'A' printed to the console.

Hint: Use the Where method and string.StartsWith inside the lambda.

Interview Questions

What is a lambda expression in C#?

Interview

A lambda expression is an anonymous function that can contain expressions or statements, used to create delegates or expression tree types.

How do lambda expressions improve LINQ queries?

Interview

Lambdas provide concise inline functions that specify query logic, making LINQ queries more readable and expressive.

Can lambda expressions capture variables from the enclosing scope?

Interview

Yes, lambdas can capture and use variables from their enclosing scope, a feature known as closures.