using System;namespace ConsoleApplication1
{class C1 { };//该式隐式从System.Object派生class Program{static void Main(string[] args){//向基类型转换不需要转型Object o = new C1();//向派生类型转换需要转型C1 c = (C1)o;}}
}

using System;namespace ConsoleApplication5
{class Class1 { };class Class2 { };class Class3 : Class2 { };class IsTest{static void Test(object o){Class1 a;Class2 b;if (o is Class1){Console.WriteLine("o is Class1");a = (Class1)o;}else if (o is Class2){Console.WriteLine("o is Class2");b = (Class2)o;}else{Console.WriteLine("o is neither Class1 nor Class2");}}static void Main(string[] args){Class1 c1 = new Class1();Class2 c2 = new Class2();Class3 c3 = new Class3();Test(c1);Test(c2);Test(c3);Test("string");Console.ReadKey();/*Output:o is Class1o is Class2o is Class2o is neither Class1 nor Class2.*/}}
}

    class Class2 { };class Class3 : Class2 { };class IsTest{static void Test(object o){Class1 a;Class2 b;Class3 c0 = new Class3();Console.WriteLine(c0 is Class2);Class2 c1 = new Class2();Console.WriteLine(c1 is Class3);//结果：True// False

using System;namespace ConsoleApplication3
{class Program{static void Main(string[] args){double a = 2;Boolean b1 = a is double;Console.WriteLine(b1);//返回True

            if (o is Class1){Class1 a = (Class1)o;

using System;namespace ConsoleApplication4
{class ClassA { }class ClassB : ClassA { }class ClassC { }class MainClass{static void Main(){object[] objArray = new object[3];objArray[0] = new ClassA();objArray[1] = new ClassB();objArray[2] = new ClassC();for (int i = 0; i < objArray.Length; ++i){ClassA s = objArray[i] as ClassA ;Console.Write("{0}:", i);if (s != null){Console.WriteLine("兼容于ClassA'");}else{Console.WriteLine("不兼容于ClassA");}}Console.ReadKey();}}
}
/*
Output:
0:兼容于ClassA'
1:兼容于ClassA'
2不兼容于ClassA*/