#      
## `Add()` method

The `HashSet<T>` generic class in the `System.Collections.Generic` namespace provides the **`Add()` method**, which can add an element to a HashSet in C#.

## Syntax

```
public bool Add (T item);
```

## Arguments

This method takes the following as input: 

* The item of type T which is to be added to the ```HashSet<T>```.

## Return values

- The method returns true if the element is successfully added. 

- The method returns false if the element is already present in the HashSet.

## Things to keep in mind

- If the number of elements in the `HashSet>T>` already equals the capacity of the `HashSet<T>` object, its capacity is automatically adjusted to accommodate the new element.

- This method is an *O(1)* operation if the number of elements is less than the capacity of the internal array.

-  If the ```HashSet<T>``` must be resized, this method becomes an *O(n)* operation, where "n" is the number of elements.

#   
## Code

We included the ```System.Collections.Generic``` namespace in our program.

using System;
using System.Collections.Generic;

class HashSetAdd
{
    static void Main()
    {
       HashSet<string> monthSet = new HashSet<string>();
       monthSet.Add("January");
       monthSet.Add("February");
       Console.WriteLine($"Added 'January' and 'February' to HashSet, Count: {monthSet.Count}");
       bool result = monthSet.Add("January");
       Console.WriteLine($"Adding 'Jaunary' again to the HashSet, result: {result}");
    }
}

#   
## Explanation

- In this example, we first created a `HashSet` of strings and have added two strings to it: `"January"` and `"February"`.

- Next, we try to add the `"January"` string to the HashSet again. Since it already exists, the `Add()` method returns `false` (which we have stored in the `result` variable).

## Output
The program prints the below output and exits.

```
Added 'January' and 'February' to HashSet, Count: 2
Adding 'Jaunary' again to the HashSet, result: False
```

How to add an element to a HashSet in C#

Use the Add() method in HashSet<T> to add elements. Returns true if added, false if duplicate.