static int[] array = { 2, 5, 6, 9, 12, 15, 18, 20, 25, 33 };
static int BinarySearch(int[] array, int x)
int left = 0, right = array.Length - 1;
int middle = (left + right) / 2;
if (x == array[middle]) return middle;
if (x < array[middle]) right = middle - 1;
public static void Main()
Console.WriteLine(BinarySearch(array, 18));