Why is my two dimensional array changing?

Question

i have the following code:

    static void Main(string[] args)
    {
        int m = 4, n = 5; 
        int[,] a = new int[m, n];

        for (int i = 0; i < a.GetLength(0); i++)
            for (int j = 0; j < a.GetLength(1); j++)
                a[i, j] = random.Next(10);


        VypisMatici(a);


        int[,] a0 = a;
        Console.WriteLine("Chessboard: ");
        for (int i = 0; i < a0.GetLength(0); i++)
        {
            for (int j = 0; j < a0.GetLength(1); j++)
            {
                if (((j % 2 == 0) && (i % 2 == 0) && (a0[i, j] % 2 == 0)) || ((j % 2 != 0) && (i % 2 != 0) && (a0[i, j] % 2 == 0)) || ((j % 2 != 0) && (i % 2 == 0) && (a0[i, j] % 2 != 0)) || ((j % 2 == 0) && (i % 2 != 0) && (a0[i, j] % 2 != 0)))
                {
                    a0[i, j]++;
                }
            }
        }



        Console.WriteLine("---------");
        for (int i = 0; i < a0.GetLength(0); i++)
        {
            for (int j = 0; j < a0.GetLength(1); j++)
                Console.Write("{0,2}, ", a0[i, j]);
            Console.WriteLine();
        }

        Console.WriteLine("Vypsání v opačném pořadí: ");
        int[,] a1 = new int[a.GetLength(0), a.GetLength(1)];
        for (int i = 0; i < a1.GetLength(0); i++)
        {
            for (int j = 0; j < a1.GetLength(1); j++)
            {
                a1[i, a1.GetLength(1) - (j + 1)] = a[i, j];
            }

        }
        VypisMatici(a1);
        Console.WriteLine("Prohození prvků na řádcích: ");
        int temp;
        int[,] a2 = a;
        for (int i = 0; i < a2.GetLength(0); i +=2)
        {
            for (int j = 0; j < a2.GetLength(1); j++)
            {
                if (a2.GetLength(0) - 1 > i)    
                {
                    temp = a2[i, j];
                    a2[i, j] = a2[i + 1, j];
                    a2[i + 1, j] = temp;
                }
            }
        }
        VypisMatici(a2);
        Console.ReadLine();
    }

    static void VypisMatici(int[,] matice)
    {
        // Vypsání matice
        for (int i = 0; i < matice.GetLength(0); i++)
        {
            for (int j = 0; j < matice.GetLength(1); j++)
                Console.Write("{0,2}, ", matice[i, j]);
            Console.WriteLine();
        }
        Console.WriteLine();
    }
}

The important code is „chessboard“ and above. The chessboard should increase some elements of array so i get array, which looks like a chessboard - odd numbers will be white square and even numbers will be black square. My problem is, that array a is after the chessboard loop same as a0. I am wondering why. (sorry for strings in czech language - actually the part in czech is not important in this problem). Sorry for my bad english. Thanks for help.

Answer 1

In the line int[,] a0 = a;, you are not copying the array, but giving it a second name (reference) to the same object in memory. So when you modify a0, a is also changed.