C# List – Add Element

C# List – Add Element with List.Add()

Use List<T>.Add() to add one element to the end of a C# List<T>. The item must be compatible with the list’s element type. For example, a List<int> accepts integers, while a List<string> accepts strings.

The Add() method changes the existing list. It does not return the added item or a new list.

C# List.Add() syntax and how it appends an element

To add an element to the C# List, use List.Add() method. The definition of of List.Add() is given below.

void List<T>.Add(T item)

Add() method returns nothing. item/element passed as the argument to Add() method should match the type of List items.

T represents the element type of the list, and item is the value to add. Add() places the new item after the current last element, so the list’s Count increases by one.

Example 1 – Add integers to a C# List with Add()

In this example, we shall shall create a List of integers, and then add items to it using Add() method.

Program.cs

using System;
using System.Collections.Generic;

class Program {
    static void Main(string[] args) {
        //empty list
        List<int> nums = new List<int>();

        //add elements to list
        nums.Add(63);
        nums.Add(58);
        nums.Add(47);
        
        //print list
        foreach (int num in nums) {
            Console.WriteLine(num);
        }
    }
}

Run the above C# program. The three items shall be added to the list.

Output

63
58
47

Each call to Add() appends one integer. The order in which the values are added is therefore the same order shown when the list is enumerated.

Add a string to a C# List<string>

The same method works with other generic list types. For a list of strings, pass a string to Add().

List<string> names = new List<string>();

names.Add("Ava");
names.Add("Noah");

Console.WriteLine(names[0]);
Console.WriteLine(names[1]);

Output

Ava
Noah

Example 2 – Add an object to a C# List

In this example, we shall add custom class objects to the given list.

We shall define a class named Car. In the Main method, we shall create a List that can contain elements of type Car. Then we shall create objects of type Car and add to the list.

Program.cs

using System;
using System.Collections.Generic;

class Program {
    static void Main(string[] args) {
        //create list
        List<Car> cars = new List<Car>();
        //add objects to the list
        cars.Add(new Car("Toyota", 1250000));
        cars.Add(new Car("Tata", 1300000));
        cars.Add(new Car("Honda", 1150000));
        
        //print
        foreach (Car car in cars) {
            Console.WriteLine(car.name + " - "+car.price);
        }
    }
}

class Car{
    public string name;
    public int price;
    public Car(string name, int price){
        this.name = name;
        this.price = price;
    }
}

Run the above C# program.

Output

Toyota - 1250000
Tata - 1300000
Honda - 1150000

Because the list is declared as List<Car>, each argument passed to Add() is a Car object.

Example 3 – Adding the wrong data type to a C# List

When you try to add an element of a different datatype, you will get an error saying argument cannot be converted.

In this example, we have initialized a list of integers. But, then we try to add an element of type string.

Program.cs

using System;
using System.Collections.Generic;

class Program {
    static void Main(string[] args) {
        //empty list
        List<int> nums = new List<int>();

        //add elements to list
        nums.Add(63);
        nums.Add(58);
        nums.Add("hello");
        
        //print list
        foreach (int num in nums) {
            Console.WriteLine(num);
        }
    }
}

Run the above C# program.

Output

D:\workspace\csharp\HelloWorld\Program.cs(10,18): error CS1503: Argument 1: cannot convert from 'string' to 'int' [D:\workspace\csharp\HelloWorld\HelloWorld.csproj]

The compiler rejects "hello" because the list was declared as List<int>. Use a value of the correct type, or use a different list type when the program genuinely needs to store different data.

Add multiple elements to a C# List with AddRange()

Add() accepts one item per call. When you already have several values in an array, list, or another compatible collection, AddRange() is the direct way to append all of them to the existing list.

list.AddRange(collection);

For example:

List<int> numbers = new List<int> { 10, 20 };
int[] moreNumbers = { 30, 40, 50 };

numbers.AddRange(moreNumbers);

foreach (int number in numbers)
{
    Console.WriteLine(number);
}

Output

10
20
30
40
50

Append another C# List with AddRange()

You can also append one list to another when both contain compatible element types. The source list is not replaced; its elements are added to the end of the destination list.

List<string> first = new List<string> { "red", "green" };
List<string> second = new List<string> { "blue", "black" };

first.AddRange(second);

Console.WriteLine(string.Join(", ", first));

Output

red, green, blue, black

Add an element at the beginning or a specific index with List.Insert()

Add() always places the item at the end. If the item must go at a particular zero-based index, use Insert(index, item). To add an item to the front of a list, insert it at index 0.

List<string> colors = new List<string> { "green", "blue" };

colors.Insert(0, "red");
colors.Insert(2, "yellow");

Console.WriteLine(string.Join(", ", colors));

Output

red, green, yellow, blue

The index passed to Insert() can range from 0 through the current Count. Using Count as the index inserts the item at the end, although Add() is clearer when appending is the only goal.

C# List.Add(), AddRange(), and Insert() compared

Method	Use it when	Position
Add(item)	You want to add one element	End of the list
AddRange(collection)	You want to add multiple elements from a compatible collection	End of the list
Insert(index, item)	You want to add one element at a specific index	The specified index

Key points for adding elements to a C# List

• Use Add() to append one item to the end of a List<T>.
• The added value must be compatible with the list’s generic type T.
• Use AddRange() when adding multiple items from another collection.
• Use Insert() when the new item belongs at the beginning or another specific index.
• Adding an item increases the list’s Count; existing items remain in the list.

In this C# Tutorial, we learned how to add an item to C# List, using List.Add() method.