Binary search algorithm find Element Index(sorted array)

using System;
class BinarySearchAlgorithm
{
  static void Main()
  {
    //Write a program that finds the index of given element in a sorted array of integers by using the binary search algorithm (find it in Wikipedia).

    int[] searchArray = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };
    Array.Sort(searchArray);

    int numToSearch = 8,
        startSearchIndex = 0,
        endSearchIndex = searchArray.Length-1,
        currentMiddle = 0;
    bool foundFlag = false;

    while (startSearchIndex <= endSearchIndex)
    {
      currentMiddle = (startSearchIndex + endSearchIndex)/2;

      if (searchArray[currentMiddle] == numToSearch)
      {
        Console.WriteLine("The index of the searched number {0} is: {1}", numToSearch, currentMiddle);
        foundFlag = true;
        break;
      }
      else if (searchArray[currentMiddle] < numToSearch)
      {
        startSearchIndex = currentMiddle + 1;
      }
      else
      {
        endSearchIndex = currentMiddle - 1;
      }
    }

    if (foundFlag == false)
      {
        Console.WriteLine("Number {0} not found in the array!", numToSearch);
      }
  }
}