C# array learning

Array Overview

C# Arrays are indexed from zero, that is, array indexes start from zero. Arrays work in C# similarly to how they work in most other popular languages. But there are some differences that should be noted.

When declaring an array, square brackets ([]) must follow the type, not the identifier. In C#, it is illegal syntax to put square brackets after an identifier.

int[] table; // not int table[];

Another detail is that the size of the array is not part of its type, but in C language it is part of the array type. This allows you to declare an array and assign to it an arbitrary array of int objects, regardless of the array length.

int[] numbers; // declare numbers as an int array of any size

numbers = new int[10]; // numbers is a 10-element array

numbers = new int[20]; // now it's a 20-element array

Declaration array

C# supports one-dimensional arrays, multi-dimensional arrays (rectangular arrays) and arrays of arrays (interleaved arrays). The following example shows how to declare arrays of different types:

One-dimensional array:

int[] numbers;

Multi-dimensional array:

string[,] names;

Array of arrays (interleaved):

byte[][] scores;

Declaring arrays (shown above) does not actually create them. In C#, arrays are objects (discussed later in this tutorial) and must be instantiated. The following example shows how to create an array:

One-dimensional array:

int[] numbers = new int[5];

Multi-dimensional array:

string[,] names = new string[5,4];

Array of arrays (interleaved):

byte[][] scores = new byte[5][];
for (int x = 0; x < scores.Length; x++)
{
scores[x ] = new byte[4];
}

You can also have larger arrays. For example, you can have a three-dimensional rectangular array:

int[,,] buttons = new int[4,5,3];

You can even mix rectangular arrays and jagged arrays. For example, the following code declares a one-dimensional array of a two-dimensional array of type int and a three-dimensional array of types.

int[][,,][,] numbers;
Initializing arrays

C# provides a simple and straightforward way to initialize an array at declaration time by enclosing the initial value in curly braces ({}). The following examples show various ways to initialize arrays of different types.

Note If the array is not initialized when declared, the array members will be automatically initialized to the default initial value of the array type. Additionally, if an array is declared as a field of a type, it will be set to the default value of null when the type is instantiated.

One-dimensional array

int[] numbers = new int[5] {1, 2, 3, 4, 5};
string[] names = new string[3] {"Matt", "Joanne", " Robert"};

The size of the array can be omitted, as follows:

int[] numbers = new int[] {1, 2, 3, 4, 5};
string[] names = new string[] {"Matt", "Joanne", "Robert"};

If an initializer is provided, you can also omit the new operator, like this:

int[] numbers = {1, 2, 3, 4, 5};
string[] names = {"Matt", "Joanne", "Robert"};

Multidimensional array

int[,] numbers = new int[3, 2] { {1 , 2}, {3, 4}, {5, 6} };
string[,] siblings = new string[2, 2] { {"Mike","Amy"}, {"Mary","Albert" } };

The size of the array can be omitted, as follows:

int[,] numbers = new int[,] { {1, 2}, {3, 4}, {5, 6} };
string[,] siblings = new string[,] { {"Mike","Amy"}, {"Mary","Albert"} };

You can also omit new if an initializer is provided Operator, as shown below:

int[,] numbers = { {1, 2}, {3, 4}, {5, 6} };
string[,] siblings = { {"Mike", "Amy "}, {"Mary", "Albert"} };

Jagged array (array of arrays)

You can initialize a jagged array as shown in the following example:

int[][] numbers = new int [2][] { new int[] {2,3,4}, new int[] {5,6,7,8,9} };

The size of the first array can be omitted, as shown below ：

int[][] numbers = new int[][] { new int[] {2,3,4}, new int[] {5,6,7,8,9} };

－ or -

int[][] numbers = { new int[] {2,3,4}, new int[] {5,6,7,8,9} };

Please note that for interleaved arrays The elements have no initialization syntax.

Accessing array members

Accessing array members can be done directly, similar to accessing array members in C/C++. For example, the following code creates an array named numbers and then assigns 5 to the fifth element of the array:

int[] numbers = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0};
numbers[4] = 5;

The following code declares a multidimensional array and assigns 5 to the member located at [1, 1]:

int[,] numbers = { { 1, 2}, {3, 4}, {5, 6}, {7, 8}, {9, 10} };
numbers[1, 1] = 5;

The following declares a one-dimensional jagged array, which contains two elements. The first element is an array of two integers, and the second element is an array of three integers:

int[][] numbers = new int[][] { new int[] {1, 2}, new int [] {3, 4, 5}
};

The following statement assigns 58 to the first element of the first array and 667 to the second element of the second array:

numbers[ 0][0] = 58;
numbers[1][1] = 667;
Arrays are objects

In C#, arrays are actually objects. System.Array is the abstract base type for all array types. You can use the properties that System.Array has as well as other class members. An example of this usage is 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 named LengthOfNumbers:

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

The System.Array class provides many useful additional methods/properties such as methods for sorting, searching, and copying arrays.

Use foreach on arrays

C# also provides the foreach statement. This statement provides a simple, clear way to iterate through the elements of an array. For example, the following code creates an array named numbers and iterates through the array using a foreach statement:

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

Due to multi-dimensional arrays, you can use the same method to iterate through elements, for example:

int[,] numbers = numbers new int[3, 2] {{9, 99}, {3, 33}, {5, 55}};
foreach(int i in numbers)
{
Console.Write("{0} ", i) ;
}

The output of this example is:

9 99 3 33 5 55

However, thanks to multidimensional arrays, using nested for loops will give you better control over the array elements.

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