BinarySearch in C#

program.cs

using System;

namespace BinarySearch
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] inputArray = new int[4] { 10, 11, 12, 13 };
            int key = 12;
            
            Console.WriteLine(BinarySearch(inputArray, key));
            Console.ReadLine();
        }

        public static object BinarySearch(int[] inputArray, int key)
        {
            int minIndex = 0;
            int maxIndex = inputArray.Length;

            while (minIndex < maxIndex)
            {
                int midIndex = (minIndex + maxIndex) / 2;

                if (inputArray[midIndex] == key)
                {
                    return midIndex;
                }
                else if (inputArray[minIndex] < key)
                {
                    minIndex = midIndex + 1;
                }
                else
                {
                    maxIndex = midIndex - 1;
                }
            }
            return null;
        }
    }
}