using System;

public delegate void ItemFoundCallback(int index);

​

public static class ItemFinder {

    public static void FindItem(string[] list, string stringToFind, ItemFoundCallback callback) {

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

            string s = list[i];

            if (s == stringToFind) {

                callback(i);

            }

        }

    }

}

​

public class Program

{

    public static void Announce(int i) {

        Console.WriteLine("String found at index {0}!",i);

    }

    public static void Main()

    {

        string[] s = {"Pikachu", "Squirtle", "Ditto", "Pikachu", "Ditto", "Dragonite"};

        ItemFinder.FindItem(s,"Pikachu",Announce);

    }

}