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Showing content from https://www.geeksforgeeks.org/c-sharp/c-sharp-add-element-to-hashset/ below:

C# | Add element to HashSet

Last Updated : 11 Jul, 2025

A

is an unordered collection of the

. It comes under

namespace. It is used in a situation where we want to prevent duplicates from being inserted in the collection. As far as performance is concerned, it is better in comparison to the list. Elements can be added to

using

.

mySet.Add(T item);

Here

is the name of the HashSet.

item: The element to add to the set.

This method returns

if the element is added to the

. If the element is already present then it returns

. Below given are some examples to understand the implementation in a better way:

// C# code to add element to HashSet
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of odd numbers
        HashSet<int> odd = new HashSet<int>();

        // Inserting elements in HashSet
        for (int i = 0; i < 5; i++) {
            odd.Add(2 * i + 1);
        }

        // Displaying the elements in the HashSet
        foreach(int i in odd)
        {
            Console.WriteLine(i);
        }
    }
}

// C# code to add element to HashSet
using System;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a HashSet of strings
        HashSet<string> mySet = new HashSet<string>();

        // Inserting elements in HashSet
        mySet.Add("Geeks");
        mySet.Add("GeeksforGeeks");
        mySet.Add("GeeksClasses");
        mySet.Add("GeeksQuiz");

        // Displaying the elements in the HashSet
        foreach(string i in mySet)
        {
            Console.WriteLine(i);
        }
    }
}

Geeks
GeeksforGeeks
GeeksClasses
GeeksQuiz

• https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1.add?view=netframework-4.7.2

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