Argument being taken as reference without "ref" keyword

Hey!

So, in my app I need to consistently multiply the elements of multiple arrays, so I created a function to do that.

The function:

Code (CSharp):

1.  
2. public static class Tools
3. {
4.     public static int[] MultiplyArrays(int[][] Arrays)
5.     {
6.  
7.         int[] ResultArray = new int[Arrays[0].Length];
8.  
9.         ResultArray = Arrays[0];
10.  
11.  
12.         for (int i = 0; i < ResultArray.Length; i++)
13.         {
14.             for (int n = 1; n < Arrays.Length; n++)
15.             {
16.                 ResultArray[i] = ResultArray[i] * Arrays[n][i];
17.             }
18.  
19.         }
20.  
21.         return ResultArray;
22.     }
23. }

Then, say I call it with the following statement in another script:

Code (CSharp):

1.  
2.         int[] array = Tools.MultiplyArrays(new int[][] { Array1, Array2 });

The values for the variable array are being returned correctly.
However, Array1 values are also being multiplied, even when I didn't call the int[][] argument as a ref.

An example:

if I call Array1 as { 10, 20 } and Array2 as { 3, 1}, I get the result array correctly as { 30, 20}, but Array1 is now also {30, 20}.

Why is that happening?
What can I do to correct this?


EDIT:

I have a similar script that sums arrays:

Code (CSharp):

1.     public static int[] SumArrays(int[][] Arrays)
2.     {
3.         int[] ResultArray = new int[Arrays[0].Length];
4.  
5.         for (int i = 0; i < ResultArray.Length; i++)
6.         {
7.             for (int n = 0; n < Arrays.Length; n++)
8.             {
9.                 ResultArray[i] += Arrays[n][i];
10.             }
11.         }
12.  
13.         return ResultArray;
14.     }

And this one works perfectly.
So, as I understand the error lies in the line

ResultArray = Arrays[0];

But it's weird to me that this line is an error, since keyword ref was'nt used.

 

I managed to find a half-answer to this.

Arrays are always references.

Based on this, I have replaced the line

Code (CSharp):

1. ResultArray = Arrays[0]

with

Code (CSharp):

1.         for (int i = 0; i < ResultArray.Length; i++)
2.         {
3.             ResultArray[i] = Arrays[0][i];
4.         }

And now the code works.

Still, I don't understand exactly why and still wonder if I can, somewhere in my code, write:

Code (CSharp):

1. int[] array1 = // something
2. int[] array2 = // something else
3.  
4. array2 = array1;

And then modify the array 1 without modifying array 2, and vice versa.

Is that possible?

 

Indeed. Arrays are objects and thus by reference.

Alternative ways to copy are:

Code (CSharp):

1. Array.Copy(arrayFrom, arrayTo, numItemsToCopy);
2. arrayTo = arrayFrom.Clone() as int[];

 

I see.

I had created a static function to copy arrays, but with the methods you mentioned, they aren't necessary.

Thanks!