How to set null a specific element of an array in C#?

Question

I´m doing a console application that removes an element of an array if a passed number by parameter appears more than one time as element of the array.

I ´ve done the main algorithm but I can´t set null the element. Here is my code:

static int[] RemoveElement(ref int[] array, int num)
{
    int i;
    for (i = 0; i < array.Length; i++)
    {
        if (array[i] == num)
        {
            array[i] = 1; //This is a temporal solution.
        }
    }

    return array;
}

Here is the Main:

static void Main(string[] args)
{
    int[] a = {10, 2, 2, 3, 4};

    Console.WriteLine("Write a number:");
    int b = int.Parse(Console.ReadLine());

    int[] arrayInts = RemoveElement(ref a, b);

    foreach (var variable in arrayInts)
    {
        Console.WriteLine(variable);
    }

    Console.ReadKey();
}

Thanks in advance! :-)

If you want to remove elements, use a List<int> instead of an array! — crashmstr
– crashmstr, Commented Jun 3, 2015 at 17:09
You could use an ArrayList instead. Then you could do array.remove(i) — Kevin Mee
– Kevin Mee, Commented Jun 3, 2015 at 17:09
@KevinMee Note: "For a strongly-typed alternative to ArrayList, consider using List<T>" — crashmstr
– crashmstr, Commented Jun 3, 2015 at 17:11
You don't need ref for how you're using that array. (ref is very rarely used in general) — Tim S.
– Tim S., Commented Jun 3, 2015 at 17:12

atlaste · Accepted Answer · 2015-06-03 17:14:34Z

1

I'm not entirely sure what you're after, but let me straighten a few things out. This should solve your issue.

If you want to set an element in an array to null, make sure the element types of the array are a reference type.

For example: int is a value type, and therefore cannot be set to null. You can however use an object, or better for integers: use the nullable-int variant: int?, and set it to null.

In short, this DOES NOT work:

int[] foo = new int[10];
foo[1] = null; // error: int is a value type

If you want to modify an array, do it in a list; even though you can realloc and copy elements of an array, it's error-prone and probably gives you issues.

So, in code:

List<int> foo = new List<int> { 1,2,3,4,5};
foo.RemoveAt(2);

If you remove a lot of elements in the middle of a List, you're probably not looking for a List.

There are data structures way more suitable for 'random removal' if that's what you want. For example, linked lists allow you to remove the middle element without moving all data around, and if you need a 'bag of values', use a HashSet or a Dictionary.

And if you still want an array...

It is of course possible, just probably not very efficient:

int[] array = new int[10]; //...
Array.Copy(array, src, array, src-1, array.Length - src - 1);
Array.Resize(ref array, array.Length-1);

answered Jun 3, 2015 at 17:14

atlaste

31.3k3 gold badges62 silver badges93 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

juharr Over a year ago

Note that int? is not a reference type. It's a struct that has special treatment when setting and comparing to null.

David Copano Jiménez Over a year ago

Thank you for the explanation! Thank you also all the people that commented :D

atlaste Over a year ago

@juharr Yes, that's why I mention object, which boxes the value type. You're right, it's a good addition.

Rahul Tripathi · Accepted Answer · 2015-06-03 17:13:21Z

0

You can use LINQ to remove repeated elements:

var intArray = new[] { 10, 2, 2, 3, 4 };
var remove = intArray.Distinct().ToArray();

Also as others have stated there is no NULL int.

Likewise you can try the same using List

List<Type> list1 = list.Distinct().ToList<Type>();

answered Jun 3, 2015 at 17:13

Rahul Tripathi

173k33 gold badges292 silver badges341 bronze badges

Collectives™ on Stack Overflow

How to set null a specific element of an array in C#?

2 Answers 2

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related