List<T>.Sort() / Reverse() / ForEach()

using System.Collections.Generic;

// Sorts the list in ascending order using the default comparer (modifies the original list).
list.Sort()

// Sorts the list using a comparison function specified with a lambda expression.
list.Sort(Comparison<T> comparison)

// Reverses the order of elements in the list (modifies the original list).
list.Reverse()

// Executes an action on every element in the list.
list.ForEach(Action<T> action)

Use Sort() to sort in ascending order, Reverse() for descending order, and ForEach() to process all elements with a lambda expression.

Program.cs

using System;
using System.Collections.Generic;

List<int> scores = new List<int> { 78, 92, 45, 88, 61 };

scores.Sort();
Console.WriteLine(string.Join(", ", scores)); // 45, 61, 78, 88, 92

scores.Reverse();
Console.WriteLine(string.Join(", ", scores)); // 92, 88, 78, 61, 45

scores.ForEach(p => Console.Write(p + " "));
Console.WriteLine();

This produces the following output:

dotnet run
45, 61, 78, 88, 92
92, 88, 78, 61, 45
92 88 78 61 45

Passing a lambda expression to Sort() lets you sort by any condition. A negative return value means a comes first; a positive return value means b comes first. Using CompareTo() keeps the code concise.

CustomSortSample.cs

using System;
using System.Collections.Generic;

List<string> names = new List<string> { "Okabe Rintaro", "Shiina Mayuri", "Makise Kurisu", "Hashida Itaru" };

// Sort by string length, shortest first
names.Sort((a, b) => a.Length.CompareTo(b.Length));
names.ForEach(n => Console.WriteLine(n));

This produces the following output:

dotnet run
Hashida Itaru
Shiina Mayuri
Makise Kurisu
Okabe Rintaro

Elements of equal length may appear in different order depending on the environment. List.Sort() does not guarantee a stable sort.

Sort() and Reverse() modify the original list in place. To keep the original order, create a copy using new List<T>() and sort the copy instead.

PreserveSample.cs

using System;
using System.Collections.Generic;

List<int> original = new List<int> { 3, 1, 4, 1, 5, 9 };
List<int> sorted = new List<int>(original);
sorted.Sort();

Console.WriteLine(string.Join(", ", original)); // 3, 1, 4, 1, 5, 9 (unchanged)
Console.WriteLine(string.Join(", ", sorted)); // 1, 1, 3, 4, 5, 9

This produces the following output:

dotnet run
3, 1, 4, 1, 5, 9
1, 1, 3, 4, 5, 9

Common Mistake: break and continue Cannot Be Used Inside ForEach()

Lambda expressions inside ForEach() do not support break or continue. If you need to exit the loop early, use a regular foreach statement instead.

using System;
using System.Collections.Generic;

// NG: break is not allowed inside ForEach() (compile error)
List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
// numbers.ForEach(n => {
//     if (n == 3) break; // CS0139: No enclosing loop out of which to break or continue
//     Console.WriteLine(n);
// });

The corrected version looks like this:

using System;
using System.Collections.Generic;

// OK: use a regular foreach statement
List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };
foreach (int n in numbers)
{
    if (n == 3) break;
    Console.WriteLine(n);
}

This produces the following output:

dotnet run
1
2

Both Sort() and Reverse() modify the original list in place. If you need to preserve the original list, create a copy first using new List<T>(originalList) before calling these methods.

ForEach() lets you write a foreach loop concisely with a lambda expression, but you cannot use break or continue inside it. If you need to exit the loop early, use a regular foreach statement instead.

For adding and removing list elements, see List<T>.Add() / Remove() / Clear().