int[] numbers = { 1, 2, 3, 4, 5 };
int lengthOfNumbers = numbers.Length;

class TestArraysClass
{
  static void Main()
  {
    // Declare and initialize an array:
    int[,] theArray = new int[5, 10];
    System.Console.WriteLine("The array has {0} dimensions.", theArray.Rank);
  }
}

 The array has 2 dimensions.

static void TestMethod1(out int[] arr)
{
  arr = new int[10];  // definite assignment of arr
}

static void TestMethod2(ref int[] arr)
{
  arr = new int[10];  // arr initialized to a different array
}

class TestOut
{
  static void FillArray(out int[] arr)
  {
    // Initialize the array:
    arr = new int[5] { 1, 2, 3, 4, 5 };
  }

  static void Main()
  {
    int[] theArray; // Initialization is not required

    // Pass the array to the callee using out:
    FillArray(out theArray);

    // Display the array elements:
    System.Console.WriteLine("Array elements are:");
    for (int i = 0; i < theArray.Length; i++)
    {
      System.Console.Write(theArray[i] + " ");
    }

    // Keep the console window open in debug mode.
    System.Console.WriteLine("Press any key to exit.");
    System.Console.ReadKey();
  }
}

    Array elements are:
    1 2 3 4 5  

class TestRef
{
  static void FillArray(ref int[] arr)
  {
    // Create the array on demand:
    if (arr == null)
    {
      arr = new int[10];
    }
    // Fill the array:
    arr[0] = 1111;
    arr[4] = 5555;
  }

  static void Main()
  {
    // Initialize the array:
    int[] theArray = { 1, 2, 3, 4, 5 };

    // Pass the array using ref:
    FillArray(ref theArray);

    // Display the updated array:
    System.Console.WriteLine("Array elements are:");
    for (int i = 0; i < theArray.Length; i++)
    {
      System.Console.Write(theArray[i] + " ");
    }

    // Keep the console window open in debug mode.
    System.Console.WriteLine("Press any key to exit.");
    System.Console.ReadKey();
  }
}

    Array elements are:
    1111 2 3 4 5555