How to add integer values to a C# list?

To add integer values to a List<int> in C#, you can use several methods including Add(), AddRange(), and collection initializer syntax. The Add() method is the most common way to add individual values one at a time.

Syntax

Following is the syntax for declaring an integer list and adding values −

List<int> listName = new List<int>();
listName.Add(value);

To add multiple values at once using AddRange() −

listName.AddRange(new int[] { value1, value2, value3 });

Using collection initializer syntax −

List<int> listName = new List<int> { value1, value2, value3 };

Using Add() Method

The Add() method appends a single integer to the end of the list −

using System;
using System.Collections.Generic;

class Program {
   public static void Main() {
      List<int> list1 = new List<int>();
      list1.Add(900);
      list1.Add(400);
      list1.Add(300);
      
      Console.WriteLine("List contains " + list1.Count + " elements:");
      foreach (int value in list1) {
         Console.WriteLine(value);
      }
   }
}

The output of the above code is −

List contains 3 elements:
900
400
300

Using AddRange() Method

The AddRange() method adds multiple integers at once from an array or another collection −

using System;
using System.Collections.Generic;

class Program {
   public static void Main() {
      List<int> list1 = new List<int>();
      list1.AddRange(new int[] { 100, 200, 300 });
      
      List<int> moreNumbers = new List<int> { 400, 500 };
      list1.AddRange(moreNumbers);
      
      Console.WriteLine("List after AddRange operations:");
      foreach (int value in list1) {
         Console.WriteLine(value);
      }
   }
}

The output of the above code is −

List after AddRange operations:
100
200
300
400
500

Using Collection Initializer

You can initialize a list with values at the time of declaration using collection initializer syntax −

using System;
using System.Collections.Generic;

class Program {
   public static void Main() {
      List<int> numbers = new List<int> { 10, 20, 30, 40, 50 };
      
      // You can still add more values after initialization
      numbers.Add(60);
      numbers.Add(70);
      
      Console.WriteLine("Numbers in the list:");
      for (int i = 0; i < numbers.Count; i++) {
         Console.WriteLine($"Index {i}: {numbers[i]}");
      }
   }
}

The output of the above code is −

Numbers in the list:
Index 0: 10
Index 1: 20
Index 2: 30
Index 3: 40
Index 4: 50
Index 5: 60
Index 6: 70

Comparison of Methods

Conclusion

Adding integer values to a C# list can be done using Add() for individual values, AddRange() for multiple values, or collection initializer syntax for initial values. Choose the method that best fits your specific use case and coding style preferences.