Lambda expression in C# (With Examples)

In previous article, I mentioned Foreach() vs Parallel.Foreach() in C# but now in this article, I have mentioned what are lambda expression in C# and how to use them with various examples using Console Application.

C# Lambda

A lambda expression is an anonymous (unnamed) function not bound to an identifier. Lambda expressions are anonymous functions that contain expressions or sequence of operators. 

All Lambda expiression usese lambda operator => which can be called as "goes to" or "become".

The lambda operator => divides a lambda expression into two parts. The left side is the input parameter and the right side is the lambda body.

Let's take a simple lambda expression example

Func<int, int> multiplyByTen = num => num * 10;

int result = multiplyByTen(5);// Returns 50

The expression num => num * 10 is a lambda expression. The => operator is called the "lambda operator".

In the above example, num is an input parameter to the anonymous function, and the return value of this function is num * 10.

A lambda expression has two forms:

Expression lambdas

A lambda expression with an expression on the right side of the => operator is called an expression lambda. An expression lambda returns the result of the expression and takes the following basic form

(input-parameters) => expression

The body of an expression lambda can consist of a method call.

Statement lambdas

A statement lambda resembles an expression lambda except that its statements are enclosed in braces, This form has an expression as its body.

(input-parameters) => { <sequence-of-statements> }

Example:

Action<string> greet = name =>
{
    string greeting = $"My Name is {name}!";
    Console.WriteLine(greeting);
};
greet("John");

// Output:
// My Name is John

C# Lambda Expression Examples

Let's take a look at few .NET Core Console app lambda expression examples, to understand it better.

Example 1

Suppose, we need to find even numbers from list of numbers, then we can simply use lambda expression (x => x% 2 ) with FindAll Method to get the list of even numbers as shown below:

using System;
using System.Collections.Generic;

namespace LambdaExpressions
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List<int> listOfNumbers = new List<int>() { 1, 4, 3, 2, 8, 6, 7, 12, 9 , 10 };
            //find all event numbers using lambda expression x => x% 2
            List<int> evenNumbers = listOfNumbers.FindAll(x => (x % 2) == 0);

            //loop through all evenUmbers
            foreach (var num in evenNumbers)
            {
                Console.Write("{0} ", num);
            }
            Console.ReadKey();
        }
    }
}

Output:

Example 2

In the above integer list let's try to find square of each number and find numbers less than 6 using Lambda expression.

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

namespace LambdaExpressions
{
    internal class Program
    {
        static void Main(string[] args)
        {
            List<int> listOfNumbers = new List<int>() { 1, 4, 3, 2, 8, 6, 7, 12, 9 , 10 };
            //using expressions x=> x*x to get sqaure of each number in list
            List<int> sqaure = listOfNumbers.Select(x => x * x).ToList();

            //print all number squares
            foreach (var num in sqaure)
            {
                Console.Write("{0} ", num);
            }
            Console.WriteLine();

            // use lambda expressions x=> x < 6 with TakeWhile to get numbers less than 6
            List<int> numberLessThanSix = listOfNumbers.TakeWhile(x => x < 6).ToList();
            //print all number less than six
            Console.Write("Numbers less than six are:");
            foreach (var num in numberLessThanSix)
            {
                Console.Write("{0} ", num);
            }
            Console.ReadKey();
        }
    }
}

Output:

1 16 9 4 64 36 49 144 81 100
Numbers less than six are:1 4 3 2

Example 3

We can also use Lambda expression with User-defined classes.

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

namespace LambdaExpressions
{
    public class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }
    internal class Program
    {
        static void Main(string[] args)
        {
            List<Student> students = new List<Student>() {
                new Student { Name = "John", Age = 10 },
                new Student { Name = "Miguel", Age = 11 },
                new Student { Name = "Brian", Age = 15 }
             };
            //get names of all students using x => x.Name
            var names = students.Select(x => x.Name);
            foreach (var name in names)
            {
                Console.WriteLine(name);
            }
        }
    }
}

Output:

John
Miguel
Brian

That's it, hope it helps.

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