C#中的readonly和const关键字

    
    public class MathUtitlity
    ...{
        public const double PI = 3.14;
        public readonly double E = 2.782;

    }

    class Program

    ...{
        static void Main(string[] args)

        ...{
            MathUtitlity math = new MathUtitlity();
            math.E = 2.5;//编译错误，不能改变已经初始化的readonly字段
            MathUtitlity.PI = 3.1456;//编译错误，不能改变已经初始化的const 字段
        }
    } 	
			

    
    //定义Person，有一个属性：name。
    public class ConstReadonly
    ...{
        public const string _const="_const";
        public readonly Person _readonly;
        public ConstReadonly()
        ...{
            _readonly = new Person();
        }
    }
    public class Person
    ...{
        public string name;
        public Person()
        ...{
            this.name = "Untitled";
        }
        public Person(string name)
        ...{
            this.name = name;
        }
    }

    class Program
    ...{
        static void Main(string[] args)
        ...{
            ConstReadonly cr = new ConstReadonly();
            Console.WriteLine(cr._readonly.name);
            cr._readonly.name = "Changed";
            Console.WriteLine(cr._readonly.name);
        }
    }

    //输出结果为：
    //Untitled
   //Changed