C# Lambda Expressions

Lambda expressions are anonymous functions with a concise syntax — the backbone of LINQ and functional C#.

1 - Syntax

// No parameters
Action greet = () => Console.WriteLine("Hello!");

// One parameter (parentheses optional)
Func<int, int> square = x => x * x;

// Multiple parameters
Func<int, int, int> add = (a, b) => a + b;

// Statement body (multiple lines)
Func<int, string> classify = n =>
{
    if (n < 0)  return "negative";
    if (n == 0) return "zero";
    return "positive";
};

2 - Capturing Variables (Closures)

int multiplier = 3;
Func<int, int> times = x => x * multiplier; // captures multiplier

Console.WriteLine(times(5));  // 15
multiplier = 10;
Console.WriteLine(times(5));  // 50 — captures by reference!

3 - Lambdas with LINQ

var numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var evens  = numbers.Where(n => n % 2 == 0);
var squared = numbers.Select(n => n * n);
var sum    = numbers.Where(n => n > 5).Sum();
var sorted = numbers.OrderByDescending(n => n);

Console.WriteLine(string.Join(", ", evens));   // 2, 4, 6, 8, 10
Console.WriteLine(sum);                        // 40