List.IndexOf() method with example in C#

C# List.IndexOf() strategy: Here, we will find out about the IndexOf() technique for List with example.

C# List.IndexOf() Method

List.IndexOf() technique is utilized to get the file of first event of a component in the rundown.

Syntax:

    int List<T>.IndexOf(T item);
    int List<T>.IndexOf(T item, int start_index);
    int List<T>.IndexOf(T item, int start_index, int count);

Parameter: the thing is a component of type T, whose first event will be returned if thing found.

• start_index is the beginning situation from where you need to discover the component in the rundown.
• tally is the all-out components from “start_index” to look through the component in the rundown.
• Return value: It returns record of the component if the component establishes in the rundown between indicated lists if the component doesn’t found in the rundown – it returns – 1.

Example:

    int list declaration:
    List<int> a = new List<int>();

    adding elements:
    a.Add(10);
    a.Add(20);
    a.Add(30);
    a.Add(40);
    a.Add(50);
    a.Add(10);
    a.Add(20);
    a.Add(30);
    a.Add(40);
    a.Add(50);
    
    Method calls:
    a.IndexOf(20)   //output: 1
    a.IndexOf(100)   //output: -1
    a.IndexOf(20, 1)   //output: 1
    a.IndexOf(100, 1)   //output: -1
    a.IndexOf(20, 1, 3)   //output: 1
    a.IndexOf(20, 0, 1)   //output: -1

C# Example to get the record a component in the rundown utilizing List.IndexOf() Method:

using System;
using System.Text;
using System.Collections.Generic;

namespace Test
{
    class Program
    {
        static void printList(List<int> lst)
        {
            //printing elements
            foreach (int item in lst)
            {
                Console.Write(item + " ");
            }
            Console.WriteLine();
        }

        static void Main(string[] args)
        {
            //integer list
            List<int> a = new List<int>();

            //adding elements
            a.Add(10);
            a.Add(20);
            a.Add(30);
            a.Add(40);
            a.Add(50);
            a.Add(10);
            a.Add(20);
            a.Add(30);
            a.Add(40);
            a.Add(50);

            //print the list
            Console.WriteLine("list elements...");
            printList(a);

            //using List.IndexOf(T item)
            //finding 20
            int index = a.IndexOf(20);
            if (index != -1)
                Console.WriteLine("20 found at " + index + " position.");
            else
                Console.WriteLine("20 does not found in the list");

            //finding 100
            index = a.IndexOf(100);
            if (index != -1)
                Console.WriteLine("100 found at " + index + " position.");
            else
                Console.WriteLine("100 does not found in the list");

            //using List.IndexOf(T item, int index)
            //finding 20
            index = a.IndexOf(20, 1); //start index is 1
            if (index != -1)
                Console.WriteLine("20 found at " + index + " position.");
            else
                Console.WriteLine("20 does not found in the list");

            //finding 100
            index = a.IndexOf(100, 1); //start index is 1
            if (index != -1)
                Console.WriteLine("100 found at " + index + " position.");
            else
                Console.WriteLine("100 does not found in the list");

            //using List.IndexOf(T item, int start_index, int count)
            //finding 20
            //search will perform from index 1 to next 3 elements
			index = a.IndexOf(20, 1, 3); 
            if (index != -1)
                Console.WriteLine("20 found at " + index + " position.");
            else
                Console.WriteLine("20 does not found in the list");

            //finding 20
			//search will perform from index 0 to next 1 element
            index = a.IndexOf(20, 0, 1); 
            if (index != -1)
                Console.WriteLine("20 found at " + index + " position.");
            else
                Console.WriteLine("20 does not found in the list");

            //hit ENTER to exit
            Console.ReadLine();
        }
    }
}

Output:

list elements...
10 20 30 40 50 10 20 30 40 50
20 found at 1 position.
100 does not found in the list
20 found at 1 position.
100 does not found in the list
20 found at 1 position.
20 does not found in the list