Array value seems to be different while in for loop compared to when it isn't

Question

I have a multidimensional array with values. I use two for loops to loop through each item and add a value to them. While in the array they return the correct value, but when it exits and I get the value it is completely different. For example:

Before loop: [[1,1],[2,2],[3,3]]
During loop: [[2,2],[3,3],[4,4]]
After loop [[50,50][65,65][90,90]]

It just seems to randomly change.

int[,] squareB = baseSquare;
int[,] squareC = baseSquare;
int[,] squareD = baseSquare;
Console.WriteLine("{0}", squareB[0, 1]);
for (int x = 0; x < sub; ++x)
{
     for (int y = 0; y < sub; ++y)
     {
          squareB[x, y] += 9;
          Console.WriteLine("{0}", squareB[x, y]);
          squareC[x, y] += 18;
          squareD[x, y] += 27;
     }
}
Console.WriteLine("{0}", squareB[0, 1]);

Magic!!! mind posting your code. so that, we can see what's wrong. — Rahul, Nov 12 '14 at 22:43
Code added, though I dunno how much use it is as you can't know what baseSquare is. It is programmatically filled. — Aurange, Nov 12 '14 at 22:47
Just to be sure; those are the outputs *every* time; correct? Its not actually *randomly* changing? — BradleyDotNET, Nov 12 '14 at 22:48
Yes they are always the same output, but they seem to just change from when it is in the loop and when it is out. — Aurange, Nov 12 '14 at 22:50

score 4 · Accepted Answer · answered Nov 12 '14 at 22:48

4

You're modifying the exact same array tree times at every single loop iteration:

      squareB[x, y] += 9;
      squareC[x, y] += 18;
      squareD[x, y] += 27;

These all change the exact same value.

answered Nov 12 '14 at 22:48

MarcinJuraszek

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There are three separate arrays. They are simply based of the same original array. – Aurange Nov 12 '14 at 22:49
1

@auragar no, [arrays are reference types](http://stackoverflow.com/questions/1533757/is-int-a-reference-type-or-a-value-type). All three variables point to the same array. – CodeCaster Nov 12 '14 at 22:50
1

Looking at your code - they are not. You're assigning `baseSquare` to all of them, which just assigns the reference - it doesn't copy the array. – MarcinJuraszek Nov 12 '14 at 22:50
Then therein lies the problem. How would one create copies and not references with arrays. – Aurange Nov 12 '14 at 22:51
1

`Array.Clone(baseSquare)` – MarcinJuraszek Nov 12 '14 at 22:51

Array value seems to be different while in for loop compared to when it isn't

1 Answers1