Confused by how arrays work in C#

Question

In the Modify method, the first line is able to modify the array but not the second, I wonder what's going on under the hood

Any answer is appreciated 👍

https://code.sololearn.com/cjQD7D8p2F25/?ref=app

Answer 1

Nick

You are creating new array but still the reference of passing array is same. That's why assigning 4 at 0th index.

You have printed the value of reference array not second array.

To print second arr return that arr then assign to numbers and then print.

Like this:

static void Main(string[] args)
{
int[] numbers = new int[3];
numbers = Modify(numbers);

foreach (int i in numbers)
Console.WriteLine(i);
}

static int[] Modify(int[] arr)
{
arr[0] = 4;
arr = new int[] { 1, 2, 3 };
return arr;
}

Answer 2

An array is a value type 🤓 [edit: turned out they aren't, I must have mixed something up 🙂] Only a copy to the array is visible in the method, it is like "arr" is a different variable. Giving it a new array does that only to "arr", not "numbers".

If you want "numbers" to change, you can pass as reference:

static void Modify(ref int[] arr)
{
arr[0] = 4;
arr = new int[] { 1, 2, 3 };
}

And call it with ref:
Modify(ref numbers);

Answer 3

Agnes Ahlberg

Arrays are value type?

Answer 4

Nick

Arrays are reference type. I don't know why she said value type.

Arrays can be passed as arguments to method parameters. Because arrays are reference types, the method can change the value of the elements.

https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/arrays/

Answer 5

Oops 😅 Yes, you are right, they are reference types 😇 I thought that I read "value type" somewhere 🤔 Sorry 🤗

Then why does it work using "ref" ? I think that it is still correct that "arr" is a different variable. And that is why the assignment does not work 😇

Thank you for pointing out my mistake 🤗💕

Answer 6

Agnes Ahlberg, don't worry, we're here to learn, don't be afraid to make mistakes

And I believe ref is pointing to the address of arr, which is probably why numbers are able to be given a new set of values