C# | Array.LastIndexOf<T>(T[], T) Method

Array.LastIndexOf<T>(T[], T) Method is used to search for the specified object. It returns the index of the last occurrence within the entire Array.

Syntax:

public static int LastIndexOf<T>(T[] array, T value);

Parameters:

array: It is a one-dimensional, zero-indexed array to search. 
value: Element whose index of last occurrence is to be returned.  

Return Value: It returns the zero-based index of type System.Int32 of the last occurrence of value within the entire array, if found otherwise it returns -1.
Exceptions This method will give ArgumentNullException if the array is null.
Below examples illustrate the use of above-discussed method:
Example 1:

CSHARP

// C# program to demonstrate
// Array.LastIndexOf<T>(T[], value<T>)
// Method
using System;

class Geeks {

    // Main Method
    public static void Main()
    {

        // Creates and initializes a new
        // Array with three elements of the
        // same value.
        string[] str = {"C", "C++", "C#", "Java",
                          "Python", "C#", "C++",
                                     "C#", "CSS"};

        // printing the Elements of an Array
        Console.WriteLine("Elements of Array: ");
        Console.WriteLine();
        foreach(string str1 in str)
        {
            Console.WriteLine(str1);
        }


        Console.Write("\nLast Occurrence of C#: ");

        // printing the last index of C#
        // using Array.LastIndexOf<T>(T[],
        // value<T>) Method
        Console.Write(Array.LastIndexOf(str, "C#"));


        Console.Write("\nLast Occurrence of C++: ");

        // printing the last index of C++
        // using Array.LastIndexOf<T>(T[],
        // value<T>) Method
        Console.Write(Array.LastIndexOf(str, "C++"));
    }
}

Output:

Elements of Array: 

C
C++
C#
Java
Python
C#
C++
C#
CSS

Last Occurrence of C#: 7
Last Occurrence of C++: 6

Example 2:

CSHARP

// C# program to demonstrate
// Array.LastIndexOf<T>(T[], value<T>)
// Method
using System;

class Geeks {

    // Main Method
    public static void Main()
    {

        // creating and initializing an array
        int[] arr = {1, 2, 3, 4, 1, 2,
                       3, 4, 2, 4, 2};

        // printing the Elements of an Array
        Console.WriteLine("Elements of Array: ");
        Console.WriteLine();
        foreach(int i in arr)
        {
            Console.WriteLine(i);
        }

        // using Array.LastIndexOf<T>(T[],
        // value<T>) Method
        // it will give runtime error as
        // array parameter is null
        Console.Write(Array.LastIndexOf(null, 1));


    }
}

Runtime Error:

Unhandled Exception: 
System.ArgumentNullException: Value cannot be null. 
Parameter name: array