#    
## `CopyTo()` method
The `HashSet<T>` generic class in the `System.Collections.Generic` namespace provides the **`CopyTo()` method** with multiple overloads, which can be used to copy a `HashSet` to an existing array in C#.

## Syntax
```
public void CopyTo (T[] array);
```

## Arguments
- This method takes a one-dimensional array as input, where the elements will be copied from `HashSet<T>`.

## Return value
This method does not return any value.

## Things to Note
- This method throws an exception if the input array is null or the number of elements in ```HashSet<T>``` is greater than the total number of spaces available in the destination array.

- This method works on one-dimensional arrays.

- This operation does not change the state of the ```HashSet<T>```.

- This is an _O(n)_ operation, where *n* is the number of elements in the ```HashSet<T>```.


## Code
We have first included the ```System.Collections.Generic``` namespace in the example below.


using System;
using System.Collections.Generic;

class HashSetCopy
{
    static void Main()
    {
        HashSet<string> months = new HashSet<string>();
        months.Add("March");
        months.Add("April");
        months.Add("May");
        months.Add("June");

        Console.WriteLine("HashSet Items : ");
        PrintSet(months);
        string[] hashSetArray = new string[4];

        Console.WriteLine("Array Items before Copy : {0}", string.Join(",", hashSetArray));
        months.CopyTo(hashSetArray);
        Console.WriteLine("Array Items after Copy : {0}", string.Join(",", hashSetArray));

    }

    private static void PrintSet(HashSet<string> set)
    {
      Console.Write("{");
      foreach (var i in set)
      {
          Console.Write(" {0}", i);
      }
      Console.WriteLine(" }");
    }
}

## Explanation
- In this example, we create a `HashSet` of strings to store month names, and add the names of four months to it: ```"March"```, ```"April"```, ```"May"```, and ```"June"```. 

- After we add the elements, we print all the elements present in the `HashSet`.

- After this, we create a new array  ```hashSetArray``` of strings with a size of 4 elements. 

* We now copy all the `HashSet` elements to this array with the ```CopyTo()``` method.

  ```
  months.CopyTo(hashSetArray);
  ```

- We then print the elements of the array, and we can observe that the array contains all the `HashSet` elements.

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

```
HashSet Items : 
{ March April May June }
Array Items before Copy : ,,,
Array Items after Copy : March,April,May,June
```


How to copy a HashSet to an existing array in C# 

Use the CopyTo() method to copy a HashSet<T> to an existing one-dimensional array in C#.