Array is affecting other array value C#

Question

static int[] scores = new int[100];
static int[] scorescopy;
public static int orderscores()
{
   scorescopy = scores;
    Array.Sort(scorescopy);
    int sortingtoolb = 0;
    return 0;
}

I am trying to get a copy of my initial array and then trying to sort that copy. However, when I use the Array.Sort() function, my first array keeps on being sorted as well, but I would like to preserve it. I tried taking away the new declaration on the scorescopy and that did not effect the result.

Also, is there a way to keep my unused variables within the array as null? (if I am not using all parts of it, I get a bunch of 0's in the beginning of the array).

I am using Visual Studio Express 2012 for Windows 8 on a system running Windows 8.1 Pro.

You need to understand the difference between reference types and value types, and specifically what this means for assignment. Chapter 1 of most C# books will cover this. — Chris Ballard
– Chris Ballard, Commented Mar 20, 2014 at 16:50
It was actually covered in Chapter 10 in my book... but since I had forgotten that it was called cloning, I failed to find the answer on my own through it and the internet. — user3439632
– user3439632, Commented Mar 20, 2014 at 17:10

Reed Copsey · Accepted Answer · 2014-03-20 16:52:30Z

6

An array, when assigned, only copies a reference to the same array in memory. You need to actually copy the values for this to work:

public static int orderscores()
{
    scorescopy = scores.ToArray(); // Using LINQ to "cheat" and make the copy simple
    Array.Sort(scorescopy);
    int sortingtoolb = 0;
    return 0;
}

Note that you can do this without LINQ via:

scorescopy = new int[scores.Length];
Array.Copy(scores, scorescopy, scores.Length);
//... rest of your code

answered Mar 20, 2014 at 16:52

Reed Copsey

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Comments

G.Y · Accepted Answer · 2014-03-20 17:04:11Z

3

The expression scorescopy = scores; duplicate the handle to the array.

if you want to create a copy of the array items you should change that line to:
scores.copyTo(scorescopy,0);

You still need to make sure scorecopy has enough room to store the items.
so you also need this expression: static int[] scorescopy = new int[scores.Length];

and now your code should like this:

static int[] scores = new int[100];
static int[] scorescopy = new int[scores.Length];

public static int orderscores()
{
    scores.copyTo(scorescopy,0);
    Array.Sort(scorescopy);
    int sortingtoolb = 0;
    return 0;
}

edited Mar 20, 2014 at 17:04

answered Mar 20, 2014 at 16:48

G.Y

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2 Comments

Reed Copsey Over a year ago

Note that this will raise an exception if scorescopy isn't allocated first.

G.Y Over a year ago

true - will fix that asap :)

Chris Ballard · Accepted Answer · 2014-03-20 16:56:31Z

2

You are getting a pointer to the same array, you want a clone:

scorescopy = (int [])scores.Clone();

edited Mar 20, 2014 at 16:56

Chris Ballard

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answered Mar 20, 2014 at 16:48

Kevin DiTraglia

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3 Comments

CathalMF Over a year ago

@ReedCopsey Yes it is valid C#. Well apart from it should be a capital C on clone();

CathalMF Over a year ago

@ReedCopsey Then don't just say its invalid. Say what is wrong. Saying it is invalid implies it is totally incorrect.

user3439632 Over a year ago

Thank you for the extremely simple solution! I had forgotten about the clone function.

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