C# Programming Guide - Arrays

1. Arrays
2. Arrays as Objects
3. Single-Dimensional Arrays
4. Multidimensional Arrays
5. Jagged Arrays
6. Using foreach with Arrays
7. Passing Arrays as Arguments
8. Passing Arrays Using ref and out
9. Implicitly Typed Arrays

https://docs.microsoft.com/en-us/dotnet/articles/csharp/programming-guide/arrays/

Arrays

You can store multiple variables of the same type in an array data structure. You declare an array by specifying the type of its elements.

type[] arrayName;

The following examples create single-dimensional, multidimensional, and jagged arrays:

C#

class LINQQueryExpressions
{
    static void Main()
    {
        
        // Specify the data source.
        int[] scores = new int[] { 97, 92, 81, 60 };

        // Define the query expression.
        IEnumerable<int> scoreQuery =
            from score in scores
            where score > 80
            select score;

        // Execute the query.
        foreach (int i in scoreQuery)
        {
            Console.Write(i + " ");
        }            
    }
}
// Output: 97 92 81

Array Overview

An array has the following properties:

• An array can be Single-Dimensional, Multidimensional or Jagged.

• The number of dimensions and the length of each dimension are established when the array instance is created. These values can't be changed during the lifetime of the instance.

• The default values of numeric array elements are set to zero, and reference elements are set to null.

• A jagged array is an array of arrays, and therefore its elements are reference types and are initialized to null.

• Arrays are zero indexed: an array with n elements is indexed from 0 to n-1.

• Array elements can be of any type, including an array type.

• Array types are reference types derived from the abstract base type Array. Since this type implements IEnumerable and IEnumerable<T>, you can use foreach iteration on all arrays in C#.

Related Sections

• Arrays as Objects

• Using foreach with Arrays

• Passing Arrays as Arguments

• Passing Arrays Using ref and out

Arrays as Objects

In C#, arrays are actually objects, and not just addressable regions of contiguous memory as in C and C++. Arrayis the abstract base type of all array types. You can use the properties, and other class members, that Array has. An example of this would be using the Length property to get the length of an array. The following code assigns the length of the numbers array, which is 5, to a variable called lengthOfNumbers:

C#

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

The Array class provides many other useful methods and properties for sorting, searching, and copying arrays.

Example

This example uses the Rank property to display the number of dimensions of an array.

C#

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);
    }
}
// Output: The array has 2 dimensions.

You can declare a single-dimensional array of five integers as shown in the following example:

C#

int[] array = new int[5];

This array contains the elements from array[0] to array[4]. The new operator is used to create the array and initialize the array elements to their default values. In this example, all the array elements are initialized to zero.

An array that stores string elements can be declared in the same way. For example:

C#

string[] stringArray = new string[6];

Array Initialization

It is possible to initialize an array upon declaration, in which case, the rank specifier is not needed because it is already supplied by the number of elements in the initialization list. For example:

C#

int[] array1 = new int[] { 1, 3, 5, 7, 9 };

A string array can be initialized in the same way. The following is a declaration of a string array where each array element is initialized by a name of a day:

C#

string[] weekDays = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };

When you initialize an array upon declaration, you can use the following shortcuts:

C#

int[] array2 = { 1, 3, 5, 7, 9 };
string[] weekDays2 = { "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" };

It is possible to declare an array variable without initialization, but you must use the new operator when you assign an array to this variable. For example:

C#

int[] array3;
array3 = new int[] { 1, 3, 5, 7, 9 };   // OK
//array3 = {1, 3, 5, 7, 9};   // Error

C# 3.0 introduces implicitly typed arrays. For more information, see Implicitly Typed Arrays.

Value Type and Reference Type Arrays

Consider the following array declaration:

C#

SomeType[] array4 = new SomeType[10];

The result of this statement depends on whether SomeType is a value type or a reference type. If it is a value type, the statement creates an array of 10 elements, each of which has the type SomeType. If SomeType is a reference type, the statement creates an array of 10 elements, each of which is initialized to a null reference.

For more information about value types and reference types, see Types.

Multidimensional Arrays

Arrays can have more than one dimension. For example, the following declaration creates a two-dimensional array of four rows and two columns.

C#

int[,] array = new int[4, 2];

The following declaration creates an array of three dimensions, 4, 2, and 3.

C#

int[, ,] array1 = new int[4, 2, 3];

Array Initialization

You can initialize the array upon declaration, as is shown in the following example.

C#

// Two-dimensional array.
int[,] array2D = new int[,] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } };
// The same array with dimensions specified.
int[,] array2Da = new int[4, 2] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } };
// A similar array with string elements.
string[,] array2Db = new string[3, 2] { { "one", "two" }, { "three", "four" },
                                        { "five", "six" } };

// Three-dimensional array.
int[, ,] array3D = new int[,,] { { { 1, 2, 3 }, { 4, 5, 6 } }, 
                                 { { 7, 8, 9 }, { 10, 11, 12 } } };
// The same array with dimensions specified.
int[, ,] array3Da = new int[2, 2, 3] { { { 1, 2, 3 }, { 4, 5, 6 } }, 
                                       { { 7, 8, 9 }, { 10, 11, 12 } } };

// Accessing array elements.
System.Console.WriteLine(array2D[0, 0]);
System.Console.WriteLine(array2D[0, 1]);
System.Console.WriteLine(array2D[1, 0]);
System.Console.WriteLine(array2D[1, 1]);
System.Console.WriteLine(array2D[3, 0]);
System.Console.WriteLine(array2Db[1, 0]);
System.Console.WriteLine(array3Da[1, 0, 1]);
System.Console.WriteLine(array3D[1, 1, 2]);

// Getting the total count of elements or the length of a given dimension.
var allLength = array3D.Length;
var total = 1;
for (int i = 0; i < array3D.Rank; i++) {
    total *= array3D.GetLength(i);
}
System.Console.WriteLine("{0} equals {1}", allLength, total);

// Output:
// 1
// 2
// 3
// 4
// 7
// three
// 8
// 12
// 12 equals 12

You also can initialize the array without specifying the rank.

C#

int[,] array4 = { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } };

If you choose to declare an array variable without initialization, you must use the new operator to assign an array to the variable. The use of new is shown in the following example.

C#

int[,] array5;
array5 = new int[,] { { 1, 2 }, { 3, 4 }, { 5, 6 }, { 7, 8 } };   // OK
//array5 = {{1,2}, {3,4}, {5,6}, {7,8}};   // Error

The following example assigns a value to a particular array element.

C#

array5[2, 1] = 25;

Similarly, the following example gets the value of a particular array element and assigns it to variable elementValue.

C#

int elementValue = array5[2, 1];

The following code example initializes the array elements to default values (except for jagged arrays).

C#

int[,] array6 = new int[10, 10];

Jagged Arrays

A jagged array is an array whose elements are arrays. The elements of a jagged array can be of different dimensions and sizes. A jagged array is sometimes called an "array of arrays." The following examples show how to declare, initialize, and access jagged arrays.

The following is a declaration of a single-dimensional array that has three elements, each of which is a single-dimensional array of integers:

C#

int[][] jaggedArray = new int[3][];

Before you can use jaggedArray, its elements must be initialized. You can initialize the elements like this:

C#

jaggedArray[0] = new int[5];
jaggedArray[1] = new int[4];
jaggedArray[2] = new int[2];

Each of the elements is a single-dimensional array of integers. The first element is an array of 5 integers, the second is an array of 4 integers, and the third is an array of 2 integers.

It is also possible to use initializers to fill the array elements with values, in which case you do not need the array size. For example:

C#

jaggedArray[0] = new int[] { 1, 3, 5, 7, 9 };
jaggedArray[1] = new int[] { 0, 2, 4, 6 };
jaggedArray[2] = new int[] { 11, 22 };

You can also initialize the array upon declaration like this:

C#

    int[][] jaggedArray2 = new int[][] 
{
    new int[] {1,3,5,7,9},
    new int[] {0,2,4,6},
    new int[] {11,22}
};

You can use the following shorthand form. Notice that you cannot omit the new operator from the elements initialization because there is no default initialization for the elements:

C#

    int[][] jaggedArray3 = 
{
    new int[] {1,3,5,7,9},
    new int[] {0,2,4,6},
    new int[] {11,22}
};

A jagged array is an array of arrays, and therefore its elements are reference types and are initialized to null.

You can access individual array elements like these examples:

C#

// Assign 77 to the second element ([1]) of the first array ([0]):
jaggedArray3[0][1] = 77;

// Assign 88 to the second element ([1]) of the third array ([2]):
jaggedArray3[2][1] = 88;

It is possible to mix jagged and multidimensional arrays. The following is a declaration and initialization of a single-dimensional jagged array that contains three two-dimensional array elements of different sizes. For more information about two-dimensional arrays, see Multidimensional Arrays.

C#

int[][,] jaggedArray4 = new int[3][,] 
{
    new int[,] { {1,3}, {5,7} },
    new int[,] { {0,2}, {4,6}, {8,10} },
    new int[,] { {11,22}, {99,88}, {0,9} } 
};

You can access individual elements as shown in this example, which displays the value of the element [1,0] of the first array (value 5):

C#

System.Console.Write("{0}", jaggedArray4[0][1, 0]);

The method Length returns the number of arrays contained in the jagged array. For example, assuming you have declared the previous array, this line:

C#

System.Console.WriteLine(jaggedArray4.Length);

returns a value of 3.

Example

This example builds an array whose elements are themselves arrays. Each one of the array elements has a different size.

C#

class ArrayTest
{
    static void Main()
    {
        // Declare the array of two elements:
        int[][] arr = new int[2][];

        // Initialize the elements:
        arr[0] = new int[5] { 1, 3, 5, 7, 9 };
        arr[1] = new int[4] { 2, 4, 6, 8 };

        // Display the array elements:
        for (int i = 0; i < arr.Length; i++)
        {
            System.Console.Write("Element({0}): ", i);

            for (int j = 0; j < arr[i].Length; j++)
            {
                System.Console.Write("{0}{1}", arr[i][j], j == (arr[i].Length - 1) ? "" : " ");
            }
            System.Console.WriteLine();            
        }
        // Keep the console window open in debug mode.
        System.Console.WriteLine("Press any key to exit.");
        System.Console.ReadKey();
    }
}
/* Output:
    Element(0): 1 3 5 7 9
    Element(1): 2 4 6 8
*/

Using foreach with Arrays

C# also provides the foreach statement. This statement provides a simple, clean way to iterate through the elements of an array or any enumerable collection. The foreach statement processes elements in the order returned by the array or collection type’s enumerator, which is usually from the 0th element to the last. For example, the following code creates an array called numbers and iterates through it with the foreach statement:

C#

int[] numbers = { 4, 5, 6, 1, 2, 3, -2, -1, 0 };
foreach (int i in numbers)
{
    System.Console.Write("{0} ", i);
}
// Output: 4 5 6 1 2 3 -2 -1 0

With multidimensional arrays, you can use the same method to iterate through the elements, for example:

C#

int[,] numbers2D = new int[3, 2] { { 9, 99 }, { 3, 33 }, { 5, 55 } };
// Or use the short form:
// int[,] numbers2D = { { 9, 99 }, { 3, 33 }, { 5, 55 } };

foreach (int i in numbers2D)
{
    System.Console.Write("{0} ", i);
}
// Output: 9 99 3 33 5 55

However, with multidimensional arrays, using a nested for loop gives you more control over the array elements.

Passing Arrays as Arguments

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

Passing Single-Dimensional Arrays As Arguments

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

C#

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

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

C#

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

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

C#

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

Example

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

C#

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

Passing Multidimensional Arrays As Arguments

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

C#

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.

C#

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

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

C#

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

Example

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

C#

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
    */

Passing Arrays Using ref and out

Like all out parameters, an out parameter of an array type must be assigned before it is used; that is, it must be assigned by the callee. For example:

C#

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

Like all ref parameters, a ref parameter of an array type must be definitely assigned by the caller. Therefore, there is no need to be definitely assigned by the callee. A ref parameter of an array type may be altered as a result of the call. For example, the array can be assigned the null value or can be initialized to a different array. For example:

C#

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

The following two examples demonstrate the difference between out and ref when used in passing arrays to methods.

Example

In this example, the array theArray is declared in the caller (the Main method), and initialized in the FillArray method. Then, the array elements are returned to the caller and displayed.

C#

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();
    }
}
    /* Output:
        Array elements are:
        1 2 3 4 5        
    */

Example

In this example, the array theArray is initialized in the caller (the Main method), and passed to the FillArray method by using the ref parameter. Some of the array elements are updated in the FillArray method. Then, the array elements are returned to the caller and displayed.

C#

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();
    }
}
    /* Output:
        Array elements are:
        1111 2 3 4 5555
    */

Implicitly Typed Arrays

You can create an implicitly-typed array in which the type of the array instance is inferred from the elements specified in the array initializer. The rules for any implicitly-typed variable also apply to implicitly-typed arrays. For more information, see Implicitly Typed Local Variables.

Implicitly-typed arrays are usually used in query expressions together with anonymous types and object and collection initializers.

The following examples show how to create an implicitly-typed array:

C#

class ImplicitlyTypedArraySample
{
    static void Main()
    {
        var a = new[] { 1, 10, 100, 1000 }; // int[]
        var b = new[] { "hello", null, "world" }; // string[]

        // single-dimension jagged array
        var c = new[]   
{  
    new[]{1,2,3,4},
    new[]{5,6,7,8}
};

        // jagged array of strings
        var d = new[]   
{
    new[]{"Luca", "Mads", "Luke", "Dinesh"},
    new[]{"Karen", "Suma", "Frances"}
};
    }
}

In the previous example, notice that with implicitly-typed arrays, no square brackets are used on the left side of the initialization statement. Note also that jagged arrays are initialized by using new [] just like single-dimension arrays.

Implicitly-typed Arrays in Object Initializers

When you create an anonymous type that contains an array, the array must be implicitly typed in the type's object initializer. In the following example, contacts is an implicitly-typed array of anonymous types, each of which contains an array named PhoneNumbers. Note that the var keyword is not used inside the object initializers.

C#

        var contacts = new[] 
{
    new {
            Name = " Eugene Zabokritski",
            PhoneNumbers = new[] { "206-555-0108", "425-555-0001" }
        },
    new {
            Name = " Hanying Feng",
            PhoneNumbers = new[] { "650-555-0199" }
        }
};