// ArrayReferenceTest.cs
// Testing the effects of passing array references
// by value and by reference.
using System;

public class ArrayReferenceTest
{
    /// <summary>
    /// ************* MAIN ***************
    /// </summary>
    /// <param name="args"></param>
    public static void Main(string[] args)
    {
        int[] array = { 1, 2, 3, 4, 5 };

        Console.WriteLine("Effects of passing reference to entire array:\n" +
                          "The values of the original array are:");

        // output original array elements 
        foreach (int value in array)
        {
            Console.Write("   {0}", value);
        }

        ModifyArray(array); // pass array reference
        Console.WriteLine("\n\nThe values of the modified array are:");

        // output modified array elements 
        foreach (int value in array)
        {
            Console.Write("   {0}", value);
        }

        Console.WriteLine("\n\nEffects of passing array element value:\n" +
                          "array[3] before ModifyElement: {0}", array[3]);

        ModifyElement(array[3]); // attempt to modify array[3]
        Console.WriteLine("array[3] after ModifyElement: {0}", array[3]);

        //
        // PASS BY REFERENCE PART
        //

        // create and initialize firstArray
        int[] firstArray = { 1, 2, 3 };

        // copy the reference in variable firstArray
        int[] firstArrayCopy = firstArray;

        Console.WriteLine("Test passing firstArray reference by value");

        Console.Write("\nContents of firstArray " +
                      "before calling FirstDouble:\n\t");

        // display contents of firstArray
        for (int i = 0; i < firstArray.Length; i++)
        {
            Console.Write("{0} ", firstArray[i]);
        }

        // pass variable firstArray by value to FirstDouble
        FirstDouble(firstArray);

        Console.Write("\n\nContents of firstArray after " +
                      "calling FirstDouble\n\t");

        // display contents of firstArray
        for (int i = 0; i < firstArray.Length; i++)
        {
            Console.Write("{0} ", firstArray[i]);
        }

        // test whether reference was changed by FirstDouble
        if (firstArray == firstArrayCopy)
            Console.WriteLine("\n\nThe references refer to the same array");
        else
            Console.WriteLine("\n\nThe references refer to different arrays");

        // create and initialize secondArray
        int[] secondArray = { 1, 2, 3 };

        // copy the reference in variable secondArray
        int[] secondArrayCopy = secondArray;

        Console.WriteLine("\nTest passing secondArray " +
                            "reference by reference");

        Console.Write("\nContents of secondArray " +
                            "before calling SecondDouble:\n\t");

        // display contents of secondArray before method call
        for (int i = 0; i < secondArray.Length; i++)
        {
            Console.Write("{0} ", secondArray[i]);
        }

        // pass variable secondArray by reference to SecondDouble
        SecondDouble(ref secondArray);

        Console.Write("\n\nContents of secondArray " +
                        "after calling SecondDouble:\n\t");

        // display contents of secondArray after method call
        for (int i = 0; i < secondArray.Length; i++)
        {
            Console.Write("{0} ", secondArray[i]);
        }

        // test whether reference was changed by SecondDouble
        if (secondArray == secondArrayCopy)
            Console.WriteLine("\n\nThe references refer to the same array");
        else
            Console.WriteLine("\n\nThe references refer to different arrays");
    }

    /// <summary>
    /// multiply each element of an array by 2 
    /// </summary>
    /// <param name="array2"></param>
    public static void ModifyArray(int[] array2)
    {
        for (int counter = 0; counter < array2.Length; counter++)
        {
            array2[counter] *= 2;
        }
    }

    /// <summary>
    /// multiply argument by 2
    /// </summary>
    /// <param name="element"></param>
    public static void ModifyElement(int element)
    {
        element *= 2;
        Console.WriteLine("Value of element in ModifyElement: {0}", element);
    }

    /// <summary>
    /// modify elements of array and attempt to modify reference
    /// </summary>
    /// <param name="array"></param>
    public static void FirstDouble(int[] array)
    {
        // double each element's value                          
        for (int i = 0; i < array.Length; i++)
        {
            array[i] *= 2;
        }

        // create new object and assign its reference to array
        array = new int[] { 11, 12, 13 };
    }

    /// <summary>
    /// modify elements of array and change reference array
    /// to refer to a new array                            
    /// </summary>
    /// <param name="array"></param>
    public static void SecondDouble(ref int[] array)
    {
        // double each element's value                     
        for (int i = 0; i < array.Length; i++)
            array[i] *= 2;

        // create new object and assign its reference to array
        array = new int[] { 11, 12, 13 };
    }
}