is和as用法

 1 namespace is_as
 2 {
 3     class Program
 4     {
 5         static void Main(string[] args)
 6         {
 7             object n = run(2);
 8             if (n is int)
 9             {
10                 Console.WriteLine((int)n);
11             }
12             else if (n is string)
13             {
14                 Console.WriteLine(n.ToString());
15             }
16             a u = new a();
17             object n2 = u;
18             b k = n2 as b;
19         }
20         public static object run(int i)
21         {
22             if (i == 1)
23             {
24                 int k = 2;
25                 return k;
26             }
27             else
28             {
29                 string ddd = "jkj";
30                 return ddd;
31             }
32         }
33     }
34 }
35 class a
36 {}
37 class b
38 { }