Arrays in C#

1. Arrays
➢Simple arrays
➢Multidimensional arrays
➢Jagged arrays
➢The Array class
➢ArrayList class
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2. Arrays
• If you need to work with multiple elements/
objects of the same type, you can use arrays
and collections.
• Arrays :
- An array stores a fixed-size sequential collection of
elements of the same type.
- An array is a data structure that contains a number
of elements of the same type.
- Reference data type.
eg: string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
int[] myNum = {10, 20, 30, 40};

3. Array Declaration & Array Initialization
• The array cannot be resized after the size is
mentioned
• Syntax
datatype[] arrayName;
where,
● datatype is used to specify the type of elements in the array.
● [ ] specifies the size of the array. The rank specifies the size of the
array.
● arrayName specifies the name of the array.
eg:
int[] myArray; // array of integers

4. Memory Allocation & Array Initialization
Initializing an Array
➢ Declaring an array does not initialize the array in the memory.
When the array variable is initialized, you can assign values to
the array.
➢ Array is a reference type, so you need to use the new keyword
to create an instance of the array. For example,
myArray = new int[4];
// Assign values
int[] myArray = new int[4] {4, 7, 11, 2};
int[] myArray = new int[] {4, 7, 11, 2};
int[] myArray = {4, 7, 11, 2};

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6. Accessing Array Elements
• After an array is declared and initialized, you can
access the array elements using an index or subscript.
• Arrays only support indexes that have integer
parameters.
eg:
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
• If you use a wrong index value where no element
exists, an exception of type
IndexOutOfRangeExceptijon iss thrown.

7. Array Length
• If you don’ t know the number of elements in
the array, you can use the Length property
for (int i = 0; i < myArray.Length; i++)
{
Console.WriteLine(myArray[i]);
}

8. Demo
using System;
namespace geeksforgeeks {
class onedarr {
// Main Method
public static void Main()
{
// declares a 1D Array of string.
string[] weekDays;
// allocating memory for days.
weekDays = new string[] {"Sun", "Mon", "Tue", "Wed",
"Thu", "Fri", "Sat"};
// Displaying Elements of array
foreach(string day in weekDays)
Console.Write(day + " ");
}
}

9. Multidimensional Arrays
• You cannot change the size after declaring an array.
• A 2-dimensional array can be thought of as a table, which
has x number of rows and y number of columns.
Declaration
int[,] a = new int[3, 3];
Thus, every element in the array a is identified by an element
name of the form a[ i , j ], where a is the name of the array, and
i and j are the subscripts that uniquely identify each element in
array a.

10. Multidimensional Arrays
• A 2-dimensional array can be thought of as a table, which has x
number of rows and y number of columns.
• Also called rectangular arrays
Declaration
int[,] twodim = new int[3, 3];
twodim[0, 0] = 1;
twodim[0, 1] = 2;
twodim[0, 2] = 3;
twodim[1, 0] = 4;
twodim[1, 1] = 5;
twodim[1, 2] = 6;
twodim[2, 0] = 7;
twodim[2, 1] = 8;
twodim[2, 2] = 9;

11. Using an array initializer
• When using an array initializer, you must
initialize every element of the array. It is
not possible to leave the initialization for
some values.

12. 2D array - Example
using System;
public class twodarr
{
public static void Main(string[] args)
{
int[ ,] arr=new int[3,3];//declaration of 2D array
arr[0,1]=10;//initialization
arr[1,2]=20;
arr[2,0]=30;
//traversal
for(int i=0;i<3;i++){
for(int j=0;j<3;j++){
Console.Write(arr[i,j]+" ");
}
Console.WriteLine();//new line at each row
}
}
}

13. Jagged Arrays - Variable sized arrays
• A jagged array is more flexible in sizing the array.
• With a jagged array every row can have a
different size.
• Array of arrays
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 };

14. Jagged array - Example
public static void Main()
{
// Declare the Jagged Array of four elements:
int[][] jagged_arr = new int[4][];
// Initialize the elements
jagged_arr[0] = new int[] {1, 2, 3, 4};
jagged_arr[1] = new int[] {11, 34, 67};
jagged_arr[2] = new int[] {89, 23};
jagged_arr[3] = new int[] {0, 45, 78, 53, 99};
// Display the array elements:
for (int n = 0; n < jagged_arr.Length; n++)
{ // Print the row number
System.Console.Write("Row : " +n + " :");
for (int k = 0; k < jagged_arr[n].Length; k++)
{
// Print the elements in the row
System.Console.Write( " "+jagged_arr[n][k]);
}
System.Console.WriteLine();
}

15. Array Class
• The Array class is the base class for all the arrays in C#.
• It is defined in the System namespace.
• The Array class provides various properties and methods
to work with arrays.
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16. Array Class
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Method / Property Purpose
Clear() Sets a range of elements to empty
values
CopyTo() Copies elements from the source
array to the destination array
GetLength() Gives the number of elements in a
given dimension of the array
GetValue() Gets the value for a given index in the
array
Length Gives the length of an array
SetValue() Sets the value for a given index in the
array
Reverse() Reverses the contents of a one
dimensional array
Sort() Sorts the elements in a one
dimensional array

17. System.Array Class - example
using System;
namespace CSharpProgram
{
class Program
{
static void Main(string[] args)
{
// Creating an array
int[] arr = new int[6] { 5, 8, 9, 25, 0, 7 };
// Creating an empty array
int[] arr2 = new int[6];
// Displaying length of array
Console.WriteLine("length of first array: "+arr.Length);
// Sorting array
Array.Sort(arr);
Console.Write("First array elements: ");
// Displaying sorted array
PrintArray(arr);
// Finding index of an array element
Console.WriteLine("nIndex position of 25 is "+Array.IndexOf(arr,25));
// Coping first array to empty array
Array.Copy(arr, arr2, arr.Length);
Console.Write("Second array elements: ");

18. System.Array Class - example - contd..
// Displaying second array
PrintArray(arr2);
Array.Reverse(arr);
Console.Write("nFirst Array elements in reverse order: ");
PrintArray(arr);
}
// User defined method for iterating array elements
static void PrintArray(int[] arr)
{
foreach (Object elem in arr)
{
Console.Write(elem+" ");
}
}
}
}

19. System.Array Class - example - contd..
// Displaying second array
PrintArray(arr2);
Array.Reverse(arr);
Console.Write("nFirst Array elements in reverse order: ");
PrintArray(arr);
}
// User defined method for iterating array elements
static void PrintArray(int[] arr)
{
foreach (Object elem in arr)
{
Console.Write(elem+" ");
}
}
}
}

20. C# - ArrayList Class
• It represents an ordered collection of an object that can be indexed
individually.
• It is basically an alternative to an array. However, unlike array you can
add and remove items from a list at a specified position using an index
and the array resizes itself automatically.
• It also allows dynamic memory allocation, adding, searching and
sorting items in the list.

21. Difference between Array and ArrayList class

24. using System;
using System.Collections;
namespace ConsoleApplication3
{
class arrlistdemo
{ static void Main(string[] args)
{
// Creates and initializes a new ArrayList.
ArrayList myAL = new ArrayList();
myAL.Add("Hello");
myAL.Add("World");
myAL.Add("!");
// Displays the properties and values of the ArrayList.
Console.WriteLine("myAL");
Console.WriteLine(" Count: "+ myAL.Count);
Console.WriteLine(" Capacity: "+ myAL.Capacity);
Console.Write(" Values:");
foreach (Object obj in myAL)
Console.Write(" "+ obj);
Console.WriteLine();
Console.ReadLine();
}
}
}
ArrayList Class - example 1

25. ArrayList Class - example 2
using System;
using System.Collections;
using System.Linq;
using System.Text;
namespace ConsoleApplication3
{
class arrlist2
{
public static void Main()
{
ArrayList arlist = new ArrayList();
arlist.Add(1);
arlist.Add("Bill");
arlist.Add("300 ");
arlist.Add(true);
arlist.Add(4.5);
arlist.Add(null);
foreach (object item in arlist)
Console.WriteLine(item + ", "); //output: 1, Bill, 300, 4.5,

26. ArrayList Class - example 2 contd..
arlist.Insert(2, "Second Item");
Console.WriteLine("After inserting second item in index 2");
foreach (var val in arlist)
Console.WriteLine(val + " , ");
Console.WriteLine("After removing null");
arlist.Remove(null); //Removes first occurance of null
foreach (var val in arlist)
Console.WriteLine(val+" , ");
Console.WriteLine("After removing val at index 4");
arlist.RemoveAt(4); //Removes element at index 4
foreach (var val in arlist)
Console.WriteLine(val + " , ");
Console.WriteLine("After removing range from 0 to 2");
arlist.RemoveRange(0, 2);//Removes two elements starting from 1st item (0
index)
foreach (var val in arlist)
Console.WriteLine(val + " , ");
Console.ReadLine();
}
}