Arrays in Csharp

8/6/2019 Arrays in Csharp

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Arrays in C#

Prepared By:

Esha Batish

Lecture No-25Date-26-04-2011


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Introduction to Arrays

An array is a collection of variables of thesame type that are referred to by a common

name.

The principal advantage of an array is that it

organizes data in such a way that it can be

easily manipulated.

Arrays can be One dimensional, Two

Dimensional or Multi-Dimensional.

Commonly used are One dimensional, Two

Dimensional. Contd..


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Although arrays in C# can be used just likearrays in many other programming languages,they have one special attribute: They areimplemented as objects. By implementingarrays as objects, several important advantages

are gained, such as they are automaticallygarbage-collected.

In C#, arrays can be declared as fixed length ordynamic.

The array name behave as constant pointer which hold the reference of first element ofarray. Contd..


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Arrays are represented using Dimensions i.e.[]

Such as : DataType[] ArrayName;DataType describe the type of elements array is

going to store in it.

In Memory, Array is used to store in sequentialmanner. (Fig.1 Arrays in Memory)

Array Name

Index ElementBase Address


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Array Declaration & Intialization

An array is declared by defining the type of elements inside the array followed by emptybrackets and a variable name in c#. Such as:

For e.g. int[] myArray;

This myArray is going to store integral valueand name of the array will hold the baseaddress of the array elements.

Memory must be allocated to hold all theelements of the array. An array is a referencetype, so memory on the heap must beallocated. Contd..


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The process of allocation of memory to

declared array is called Array Initialization.

Initialization is done with new keyword such

as

myArray=new int[4];

The Declaration and initialization can be done

in single line also:

int[] myArray=new int[4];

This statement will force compiler to instruct

Operating System to allocation memory for 4

elements; each having 4bytes to store. Contd..


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Memory Representation

Name of the array is value type but it isallocated memory using new keyword so

memory allocated is on Heap.(Fig2.Memory

for myArray). Its a Single-Dimension Array.


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You can also assign values to every array

element using an array initializer. Array

initializers can be used only while declaring an

array variable, not after the array is declared:

int[] myArray = new int[] {4, 7, 11, 2};

In this case there is no need to specify the size

as size is evaluated with number of elements

passed in {}.

Using curly brackets you can write the arraydeclaration and initialization. Contd..


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int[] myArray = {4, 7, 11, 2};

Accessing Array Elements: Elements of anarray is accessed using index element in

dimensions.

int[] myArray = new int[] {4, 7, 11, 2}; int v1 = myArray[0]; // read first element

int v2 = myArray[1]; // read second element

myArray[3] = 44; // change fourth element

Contd..


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If you use a wrong indexer value where no

element exists, an exception of type

IndexOutOfRangeException is thrown.

If you don t know the number of elements in

the array, you can use the Length property that

is used in this for statement:

for (int i = 0; i < myArray.Length; i++)

{

Console.WriteLine(myArray[i]);

} Contd..


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Instead of using a for statement to iterate

through all elements of the array, you can alsouse the foreach statement:

foreach (int val in myArray)

{ Console.WriteLine(val);

}


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Using Reference TypesIn stead of declaring arrays of predefinedtypes, you can also declare arrays of custom

types. Lets Person is a user defined class, we

can create array of this class such as:

Person[] Per = new Person[2];

This array will hold memory for the data of

objects of Person class.

If elements of an array is of reference type

then memory should be allocated, otherwise

NullReferenceException is thrown. Contd..


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You can allocate every element of the array byusing an indexer starting from 0:

Per[0] = new Per ();

Per[1] = new Per(); e.g.

class Program

{

static void Main(string[] args)

{

person[] myPerson = new person[2];myPerson[0] = new person(3);

myPerson[1] = new person(4); Contd..


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myPerson[0].dis();

myPerson[1].dis();

Console.ReadKey();

}

}

class person{

int x;

public person(int x){

this.x = x;

} Contd..


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public void dis()

{Console.WriteLine(x);

}

}

Output:

3

4


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Memory Representation


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Multi-Dimensional Array

Ordinary arrays (also known as one -dimensional arrays) are indexed by a single

integer. A multidimensional array is indexed

by two or more integers. Array with 2dimension usually represent rows and

columns.

A is a 2d array.


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Declaring this two - dimensional array with C#

is done by putting a comma inside the

brackets. The array is initialized by specifying

the size of every dimension (also known as

rank). Then the array elements can be accessed

by using two integers with the indexer: int[,] a= new int[3, 3];

Here 2D array contains 3 rows and 3 columns.

Values can be initialize as: Contd..


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a[0,0]=2;

a[2,3]=9; Another way to initialize 2D array is:

int[,] a = {

{1, 2, 3},

{4, 5, 6},

{7, 8, 9}

};

When using an array initializer, you mustinitialize every element of the array. It is notpossible to leave the initialization of some valuesfor later.


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Three-Dimensional Array

By using two commas inside the brackets, youcan declare a three - dimensional array:

int[,,] threedim = {

{ { 1, 2 }, { 3, 4 } },

{ { 5, 6 }, { 7, 8 } },

{ { 9, 10 }, { 11, 12 } }

};

Console.WriteLine(threedim[0, 1, 1]);

Contd..


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Jagged Arrays

A jagged array is more flexible in sizing thearray. With a jagged array every row can have

a different size.

Each row of jagged array can have differentnumber of elements. Lets compare with 2D

arrays.


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A jagged array is declared by placing one pair ofopening and closing brackets after another. With

the initialization of the jagged array, only the sizethat defines the number of rows in the first pair ofbrackets is set. The second brackets that define thenumber of elements inside the row are kept empty

because every row has a different number of elements. Next, the element number of the rowscan be set for every row:

int[][] jagged = new int[3][];

jagged[0] = new int[2] { 1, 2 };

jagged[1] = new int[6] { 3, 4, 5, 6, 7, 8 };

jagged[2] = new int[3] { 9, 10, 11 };


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Iterating through all elements of a jagged arraycan be done with nested for loops. In the outer for

loop every row is iterated, and the inner for loopiterates through every element inside a row.

for (int row = 0; row < jagged.Length; row++)

{ for (int element = 0; element

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