Lambda Expressions in C#

A lambda expression in C# is an anonymous function that provides a concise way to write inline functions. Lambda expressions use the => operator, read as "goes to", which separates the input parameters from the expression body.

Lambda expressions are commonly used with LINQ methods, event handlers, and delegates to create short, readable code without defining separate methods.

Syntax

Following is the basic syntax for lambda expressions −

(input-parameters) => expression

For single parameter, parentheses are optional −

x => x * 2

For multiple statements, use curly braces −

(x, y) => { 
    int sum = x + y; 
    return sum * 2; 
}

Using Lambda with List Methods

Example

Here we find the first occurrence of an element greater than 50 from a list −

using System;
using System.Collections.Generic;

class Demo {
    static void Main() {
        List<int> list = new List<int> { 44, 6, 34, 23, 78 };

        int res = list.FindIndex(x => x > 50);
        Console.WriteLine("Index: " + res);
        
        // Find the actual element
        int element = list.Find(x => x > 50);
        Console.WriteLine("Element: " + element);
    }
}

The output of the above code is −

Index: 4
Element: 78

Using Lambda with LINQ

Example

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

class Program {
    static void Main() {
        List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        
        // Filter even numbers
        var evenNumbers = numbers.Where(x => x % 2 == 0).ToList();
        Console.WriteLine("Even numbers: " + string.Join(", ", evenNumbers));
        
        // Square each number
        var squares = numbers.Select(x => x * x).ToList();
        Console.WriteLine("Squares: " + string.Join(", ", squares));
        
        // Sum of numbers greater than 5
        int sum = numbers.Where(x => x > 5).Sum();
        Console.WriteLine("Sum of numbers > 5: " + sum);
    }
}

The output of the above code is −

Even numbers: 2, 4, 6, 8, 10
Squares: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100
Sum of numbers > 5: 30

Lambda with Multiple Parameters

Example

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

class Program {
    static void Main() {
        List<string> words = new List<string> { "apple", "banana", "cherry", "date" };
        
        // Sort by length, then alphabetically
        var sorted = words.OrderBy(w => w.Length).ThenBy(w => w).ToList();
        Console.WriteLine("Sorted: " + string.Join(", ", sorted));
        
        // Custom comparison using multiple parameters
        Func<int, int, int> add = (x, y) => x + y;
        Console.WriteLine("5 + 3 = " + add(5, 3));
        
        Func<int, int, bool> isGreater = (x, y) => x > y;
        Console.WriteLine("10 > 7: " + isGreater(10, 7));
    }
}

The output of the above code is −

Sorted: date, apple, banana, cherry
5 + 3 = 8
10 > 7: True

Lambda vs Anonymous Methods

Conclusion

Lambda expressions in C# provide a concise way to create anonymous functions using the => operator. They are essential for LINQ operations, functional programming patterns, and creating clean, readable code when working with collections and delegates.