C# List Find

Last modified April 11, 2025

This tutorial illustrates how to locate elements in a C# List using the Find, FindLast, FindAll, FindIndex, and FindLastIndex methods.

In C#, a List is a dynamic collection that holds elements of the same type, accessible by their index positions.

C# List Find

The Find method retrieves the first element in a List that satisfies a specified condition, known as a predicate.

A predicate is a function that takes a single argument and returns a boolean value, indicating whether the element meets the condition.

public T? Find(Predicate match);

The Find method accepts a Predicate<T> delegate, which defines the condition to match.

Program.cs

var words = new List<string> { “sky”, “cup”, “new”, “war”, “wrong”, “crypto”, “forest”, “water”, “cup” };

var vals = new List<int> { -2, -1, 3, 0, 1, 2, 1, 4, -2, 2, 1 };

string? e = words.Find(e => e.StartsWith(“w”)); Console.WriteLine(e);

int n = vals.Find(e => e > 0); Console.WriteLine(n);

This example demonstrates finding the first word starting with ‘w’ in a list of strings and the first positive integer in a list of numbers.

string? e = words.Find(e => e.StartsWith(“w”));

Here, the predicate is a lambda expression that checks if a word begins with ‘w’.

$ dotnet run war 3

C# List FindLast

The FindLast method returns the last element in a List that matches the given predicate.

public T? FindLast(Predicate match);

This defines the method’s signature.

Program.cs

var words = new List<string> { “sky”, “cup”, “new”, “war”, “wrong”, “crypto”, “forest”, “water”, “cup” };

var vals = new List<int> { -2, -1, 3, 0, 1, 2, 1, 4, -2, 2, 1 };

string? e = words.FindLast(e => e.StartsWith(“w”)); Console.WriteLine(e);

int n = vals.FindLast(e => e > 0); Console.WriteLine(n);

This program identifies the last word starting with ‘w’ in a list of strings and the last positive integer in a list of numbers.

$ dotnet run water 1

C# List FindAll

The FindAll method retrieves all elements in a List that satisfy the specified predicate, returning them as a new List.

Program.cs

var words = new List<string> { “sky”, “cup”, “new”, “war”, “wrong”, “crypto”, “forest”, “water”, “cup” };

var vals = new List<int> { -2, -1, 3, 0, 1, 2, 1, 4, -2, 2, 1 };

List<string> res = words.FindAll(e => e.StartsWith(“w”)); Console.WriteLine(string.Join(’,’, res));

List<int> res2 = vals.FindAll(e => e > 0); Console.WriteLine(string.Join(’,’, res2));

This example collects all words starting with ‘w’ from a list of strings and all positive integers from a list of numbers, then displays them as comma-separated strings.

$ dotnet run war,wrong,water 3,1,2,1,4,2,1

C# List FindIndex

The FindIndex method returns the zero-based index of the first element that matches the predicate. If no element is found, it returns -1.

public int FindIndex(Predicate match); public int FindIndex(int startIndex, Predicate match); public int FindIndex(int startIndex, int count, Predicate match);

These overloaded methods allow specifying a starting index and, optionally, the number of elements to search.

Program.cs

var words = new List<string> { “sky”, “cup”, “new”, “war”, “wrong”, “crypto”, “forest”, “water”, “cup” };

int n = words.FindIndex(e => e.StartsWith(“w”)); Console.WriteLine($“The index of the first word starting with ‘w’ is {n}”);

int n2 = words.FindIndex(5, e => e.StartsWith(“w”)); Console.WriteLine($“The index of the first word starting with ‘w’ after index 5 is {n2}”);

This program finds the index of the first word starting with ‘w’ from the beginning of the list and from index 5 onward.

$ dotnet run The index of the first word starting with ‘w’ is 3 The index of the first word starting with ‘w’ after index 5 is 7

C# List FindLastIndex

The FindLastIndex method returns the zero-based index of the last element that matches the predicate. If no match is found, it returns -1.

public int FindLastIndex(Predicate<T> match); public int FindLastIndex(int startIndex, Predicate<T> match); public int FindLastIndex(int startIndex, int count, Predicate<T> match);

These are the method signatures, allowing control over the search range.

Program.cs

var words = new List<string> { “sky”, “cup”, “new”, “war”, “wrong”, “crypto”, “forest”, “water”, “cup” };

int n = words.FindLastIndex(e => e.StartsWith(“w”)); Console.WriteLine($“The index of the last word starting with ‘w’ is {n}”);

int n2 = words.FindLastIndex(5, e => e.StartsWith(“w”)); Console.WriteLine($“The index of the last word starting with ‘w’ up to index 5 is {n2}”);

This example locates the index of the last word starting with ‘w’ in the entire list and the last one up to index 5.

$ dotnet run The index of the last word starting with ‘w’ is 7 The index of the last word starting with ‘w’ up to index 5 is 4

Source

List Find method

This tutorial has demonstrated how to locate elements in a C# List using various finding methods.

Author

My name is Jan Bodnar, and I am a dedicated programmer with extensive experience. Since 2007, I have been creating programming tutorials, authoring over 1,400 articles and 8 e-books. With more than a decade of teaching programming, I am committed to sharing my knowledge.

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