Find a specific element in a C# List

In C#, you can find specific elements in a List<T> using various built-in methods. The most common approach is using the Find() method with a lambda expression to specify search criteria.

Syntax

Following is the syntax for using the Find() method −

T element = list.Find(predicate);

Where predicate is a lambda expression that returns true for the element you want to find.

Using Find() Method

The Find() method returns the first element that matches the specified condition. If no element is found, it returns the default value for the type (0 for int, null for reference types).

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      List<int> myList = new List<int>() {
         5, 10, 17, 19, 23, 33
      };
      
      Console.WriteLine("List:");
      foreach(int i in myList) {
         Console.WriteLine(i);
      }
      
      int val = myList.Find(item => item % 2 == 0);
      Console.WriteLine("First even number: " + val);
      
      int largeVal = myList.Find(item => item > 20);
      Console.WriteLine("First number greater than 20: " + largeVal);
   }
}

The output of the above code is −

List:
5
10
17
19
23
33
First even number: 10
First number greater than 20: 23

Using FindAll() Method

To find all elements that match a condition, use the FindAll() method, which returns a new list containing all matching elements −

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      List<int> numbers = new List<int>() {
         2, 8, 15, 22, 27, 30, 45
      };
      
      List<int> evenNumbers = numbers.FindAll(x => x % 2 == 0);
      Console.WriteLine("Even numbers:");
      foreach(int num in evenNumbers) {
         Console.WriteLine(num);
      }
      
      List<int> numbersAbove20 = numbers.FindAll(x => x > 20);
      Console.WriteLine("\nNumbers greater than 20:");
      foreach(int num in numbersAbove20) {
         Console.WriteLine(num);
      }
   }
}

The output of the above code is −

Even numbers:
2
8
22
30

Numbers greater than 20:
22
27
30
45

Using Contains() Method

To check if a list contains a specific value, use the Contains() method, which returns true or false −

Example

using System;
using System.Collections.Generic;

class Demo {
   static void Main() {
      List<string> fruits = new List<string>() {
         "Apple", "Banana", "Cherry", "Date"
      };
      
      Console.WriteLine("Fruits list: " + string.Join(", ", fruits));
      
      bool hasApple = fruits.Contains("Apple");
      bool hasGrape = fruits.Contains("Grape");
      
      Console.WriteLine("Contains Apple: " + hasApple);
      Console.WriteLine("Contains Grape: " + hasGrape);
   }
}

The output of the above code is −

Fruits list: Apple, Banana, Cherry, Date
Contains Apple: True
Contains Grape: False

Comparison of Search Methods

Conclusion

C# provides multiple methods to find elements in a List: Find() for the first match, FindAll() for all matches, and Contains() to check existence. These methods use lambda expressions or direct value comparison to locate specific elements efficiently.