1 int[] a = new int[20] { 2, 3, 6, 7, 12, 18, 19, 21, 25, 28, 30, 33, 37, 39, 42, 45, 47, 49, 50, 51 }; 2             int x = 18, i; 3             string j, k; 4             var d = find(a, x, 0, 19); 5             if (d == -1) 6             { 7                 k = String.Format("未找到{0}", x); 8             } 9             else10             {11                 for (i = 0; i < 20; i++)12                 {13                     if ((i = d) > 0)14                     {15                         j = String.Format("{0}是第{1}个数\n", x, i + 1);16                         break;17                     }18                 }19             }

find方法如下：

1 int find(int[] a, int x, int n, int m)2         {3             int i;4             if (n > m) return -1;5             i = (n + m) / 2;6             if (a[i] == x) return i;7             if (a[i] > x) return find(a, x, n, i - 1);8             return find(a, x, i + 1, m);9         }

可以输出j

  显示查找结果

    good luck ----------