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Passing Arrays as Arguments (C# Programming Guide)

Arrays can be passed as arguments to method parameters. Because arrays are reference types, the method can change the value of the elements.

You can pass an initialized single-dimensional array to a method. For example, the following statement sends an array to a print method.


int[] theArray = { 1, 3, 5, 7, 9 };
PrintArray(theArray);


The following code shows a partial implementation of the print method.


void PrintArray(int[] arr)
{
    // Method code.
}


You can initialize and pass a new array in one step, as is shown in the following example.


PrintArray(new int[] { 1, 3, 5, 7, 9 });


Description

In the following example, an array of strings is initialized and passed as an argument to a PrintArray method for strings. The method displays the elements of the array. Next, methods ChangeArray and ChangeArrayElement are called to demonstrate that sending an array argument by value does not prevent changes to the array elements.

Code


class ArrayClass
{
    static void PrintArray(string[] arr)
    {
        for (int i = 0; i < arr.Length; i++)
        {
            System.Console.Write(arr[i] + "{0}", i < arr.Length - 1 ? " " : "");
        }
        System.Console.WriteLine();
    }

    static void ChangeArray(string[] arr)
    {
        // The following attempt to reverse the array does not persist when
        // the method returns, because arr is a value parameter.
        arr = (arr.Reverse()).ToArray();
        // The following statement displays Sat as the first element in the array.
        System.Console.WriteLine("arr[0] is {0} in ChangeArray.", arr[0]);
    }

    static void ChangeArrayElements(string[] arr)
    {
        // The following assignments change the value of individual array 
        // elements. 
        arr[0] = "Sat";
        arr[1] = "Fri";
        arr[2] = "Thu";
        // The following statement again displays Sat as the first element
        // in the array arr, inside the called method.
        System.Console.WriteLine("arr[0] is {0} in ChangeArrayElements.", arr[0]);
    }

    static void Main()
    {
        // Declare and initialize an array.
        string[] weekDays = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };

        // Pass the array as an argument to PrintArray.
        PrintArray(weekDays);

        // ChangeArray tries to change the array by assigning something new
        // to the array in the method. 
        ChangeArray(weekDays);

        // Print the array again, to verify that it has not been changed.
        System.Console.WriteLine("Array weekDays after the call to ChangeArray:");
        PrintArray(weekDays);
        System.Console.WriteLine();

        // ChangeArrayElements assigns new values to individual array
        // elements.
        ChangeArrayElements(weekDays);

        // The changes to individual elements persist after the method returns.
        // Print the array, to verify that it has been changed.
        System.Console.WriteLine("Array weekDays after the call to ChangeArrayElements:");
        PrintArray(weekDays);
    }
}
// Output: 
// Sun Mon Tue Wed Thu Fri Sat
// arr[0] is Sat in ChangeArray.
// Array weekDays after the call to ChangeArray:
// Sun Mon Tue Wed Thu Fri Sat
// 
// arr[0] is Sat in ChangeArrayElements.
// Array weekDays after the call to ChangeArrayElements:
// Sat Fri Thu Wed Thu Fri Sat


You pass an initialized multidimensional array to a method in the same way that you pass a one-dimensional array.


int[,] theArray = { { 1, 2 }, { 2, 3 }, { 3, 4 } };
Print2DArray(theArray);


The following code shows a partial declaration of a print method that accepts a two-dimensional array as its argument.


void Print2DArray(int[,] arr)
{
    // Method code.
}


You can initialize and pass a new array in one step, as is shown in the following example.


Print2DArray(new int[,] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } });


Description

In the following example, a two-dimensional array of integers is initialized and passed to the Print2DArray method. The method displays the elements of the array.

Code


class ArrayClass2D
{
    static void Print2DArray(int[,] arr)
    {
        // Display the array elements.
        for (int i = 0; i < arr.GetLength(0); i++)
        {
            for (int j = 0; j < arr.GetLength(1); j++)
            {
                System.Console.WriteLine("Element({0},{1})={2}", i, j, arr[i, j]);
            }
        }
    }
    static void Main()
    {
        // Pass the array as an argument.
        Print2DArray(new int[,] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } });

        // Keep the console window open in debug mode.
        System.Console.WriteLine("Press any key to exit.");
        System.Console.ReadKey();
    }
}
    /* Output:
        Element(0,0)=1
        Element(0,1)=2
        Element(1,0)=3
        Element(1,1)=4
        Element(2,0)=5
        Element(2,1)=6
        Element(3,0)=7
        Element(3,1)=8
    */


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