Array.IndexOf Method

using System;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a string array with 3 elements having the same value.
            String[] strings = { "the", "quick", "brown", "fox", "jumps",
                            "over", "the", "lazy", "dog", "in", "the",
                            "barn" };

            // Display the elements of the array.
            Console.WriteLine("The array contains the following values:");
            for (int i = strings.GetLowerBound(0); i <= strings.GetUpperBound(0); i++)
                Console.WriteLine("   [{0,2}]: {1}", i, strings[i]);

            // Search for the first occurrence of the duplicated value.
            String searchString = "the";
            int index = Array.IndexOf(strings, searchString);
            Console.WriteLine("The first occurrence of \"{0}\" is at index {1}.",
                              searchString, index);

            // Search for the first occurrence of the duplicated value in the last section of the array.
            index = Array.IndexOf(strings, searchString, 4);
            Console.WriteLine("The first occurrence of \"{0}\" between index 4 and the end is at index {1}.",
                              searchString, index);

            // Search for the first occurrence of the duplicated value in a section of the array.
            int position = index + 1;
            index = Array.IndexOf(strings, searchString, position, strings.GetUpperBound(0) - position + 1);
            Console.WriteLine("The first occurrence of \"{0}\" between index {1} and index {2} is at index {3}.",
                              searchString, position, strings.GetUpperBound(0), index);
        }
    }
}

ผลการรัน

The array contains the following values:
   [ 0]: the
   [ 1]: quick
   [ 2]: brown
   [ 3]: fox
   [ 4]: jumps
   [ 5]: over
   [ 6]: the
   [ 7]: lazy
   [ 8]: dog
   [ 9]: in
   [10]: the
   [11]: barn
The first occurrence of "the" is at index 0.
The first occurrence of "the" between index 4 and the end is at index 6.
The first occurrence of "the" between index 7 and index 11 is at index 10.

แต่ถ้าค้นหาไม่เจอจะคืนค่าเป็น -1