原理很简单，二叉树的原理

        public static void erfen(int[] array, int val)
        {
            int leftIndex = 0;//查找起始下标
            int rightIndex = array.Length - 1;//数组终点下标，即最坏情况
            int currentIndex = 0;//当前查找的下标
            Array.Sort(array);//先升序排序
            //等起始<=终点时，可以继续查找
            while (leftIndex <= rightIndex)
            {
                currentIndex = (leftIndex + rightIndex) / 2;
                if (array[currentIndex] < val)
                {
                    leftIndex = currentIndex+1;
                    Console.WriteLine(string.Format("没找到！从下标{0}开始往后找！",currentIndex+1));
                }
                else if (array[currentIndex] > val)
                {
                    rightIndex = currentIndex-1;
                    Console.WriteLine(string.Format("没找到！从下标{0}开始往前找！",currentIndex-1));
                }
                else
                {
                    Console.WriteLine(string.Format("找到了！{0}在数组中的下标是{1}", val, currentIndex));
                    break;
                }
            }
        }