C# | Get or set the element at the specified index in ArrayList

ArrayList.Item[Int32] Property is used to get or set the element at the specified index in ArrayList. Syntax:

public virtual object this[int index] { get; set; }

Here, index is the zero-based index of the element to get or set. Return Value: It returns the element of Object type at the specified index. Exception: This property will throw ArgumentOutOfRangeException if the index is less than zero or is equal to or greater than Count. Below programs illustrate the use of above-discussed property: Example 1:

CSharp

// C# code to get or set the element at
// the specified index in ArrayList
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        myList.Add("A");
        myList.Add("B");
        myList.Add("C");
        myList.Add("D");
        myList.Add("E");
        myList.Add("F");

        // Displaying the elements
        // in the ArrayList
        foreach(string str in myList)
        {
            Console.WriteLine(str);
        }

        Console.WriteLine("After Item[int32] Property: ");

        // setting the value at index 2
        myList[2] = "Z";

        // Displaying the elements
        // in the ArrayList
        foreach(string str in myList)
        {
            Console.WriteLine(str);
        }
    }
}

Output:

A
B
C
D
E
F
After Item[int32] Property: 
A
B
Z
D
E
F

Example 2:

CSharp

// C# code to get or set the element at
// the specified index in ArrayList
using System;
using System.Collections;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        // Adding elements to ArrayList
        myList.Add(2);
        myList.Add(4);
        myList.Add(6);
        myList.Add(8);
        myList.Add(10);
        myList.Add(12);
        myList.Add(14);
        myList.Add(16);
        myList.Add(18);
        myList.Add(20);

        // Displaying the elements
        // in the ArrayList
        foreach(int i in myList)
        {
            Console.WriteLine(i);
        }

        Console.WriteLine("After Item[int32] Property: ");

        // setting the value at index 8
        // this will give error as index
        // is greater than count
        myList[10] = 56;

        // Displaying the elements
        // in the ArrayList
        foreach(int j in myList)
        {
            Console.WriteLine(j);
        }
    }
}

Runtime Error:

Unhandled Exception: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

Time complexity: O(n) for traversing ArrayList

Auxiliary Space: O(n) where n is the size of the ArrayList

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.item?view=netframework-4.7.2