第十五节 常量const 、 枚举enum 、结构struct 值类型和引用类型

案例1：常量   const  

class Program
    {
        static void Main(string[] args)
        {
            //在变量前加入const 关键字意味着他就是一个常量
            //如果我们在编写程序的时候希望一个变量不能被改变，我们就定义它为常量
            //常量的标识符通常全部都是大写,程序员看到全部是大写的标识符就能明白它是一个常量
            const  double PI= 3.14;
            //一旦定义为常量意味着它的值就不能改变
            
            //PI = 3.24;

            Console.ReadKey();
        }
    }

————————————————————————————————————————————————————

案例2.1 枚举

namespace e2
{       //枚举的定义方式
       //访问修饰符 enum 枚举名
       //{
            //枚举1
            //枚举2
            //..........

        //}
   
        //枚举类型的作用就是限定取值范围,比如说性别男和女
        //枚举不能包含方法
        public enum Genders
        { 
            Male,
            Female
        
        }

    class Student
    {
        private Genders gender;
        public Genders Gender
        {
            set { gender = value; }
            get { return gender; }
        }

        public void Display()
        {
            Console.Write(gender);
        
        }
    }
   
}


——————————————————————————————————————————————————————————

案例2.2 

namespace e2
{
    class Program
    {
        static void Main(string[] args)
        {
            Student stu= new Student();
            stu.Gender =Genders.Male;
            stu.Display();
          
            Console.ReadKey();
            
        }
    }
}

——————————————————————————————————————————————————————————————————————————————————————————————————————————————

案例3 枚举转换

namespace e3
{
    public enum NIIT
    { 
        MMS1=3,
        MMS2=4,
        MMS3=5,
        MMS4=6
    }


    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("{0}", (int)NIIT.MMS1);//索引默认为0，也可自定义！

            Console.WriteLine("枚举转字符串:{0}",NIIT.MMS3.ToString());
            NIIT m3 = (NIIT)Enum.Parse(typeof(NIIT), "MMS3");


            Console.WriteLine("字符串常量转枚举:{0}",m3);
            Console.ReadKey();
        }
    }
}

————————————————————————————————————————————————————————

案例4 枚举就是自定义数据类型

namespace e4
{
    public enum TIME  //枚举就是自定义的数据类型！！！
    {
        time1 = 1,
        time2 = 2,
        time3 = 3,
        time4 = 4,
        time5 = 5,
        time6 = 6,
        time7 = 7,
    }

    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("请输入:(1-7)");
            int a=Convert.ToInt32(Console.ReadLine());

            TIME time = (TIME)a;  //枚举就是自定义的数据类型！！！
                
                switch (time)
                {
                        case TIME.time1: 
                        case TIME.time2: 
                        case TIME.time3: 
                        case TIME.time4: 
                        case TIME.time5: 
                        Console.WriteLine("需要工作,泪奔......."); break;
                        case TIME.time6: 
                        case TIME.time7:
                        Console.WriteLine("我喜欢周末!!!"); break;
                        default: Console.WriteLine("输入错误");break;

                }
                Console.ReadKey();
         
        }          
          
    }
    

——————————————————————————————————————————————————————————

案例5结构

namespace e5
{
    public struct StudentStruct
    {
        //结构 中不允许赋初始值给他的成员
        public string name;
        public int age;
        public string hobby;
        public int populraity;

        //结构不允许有默认函数！
        //public StudentStruct()
        //{ 
        //}

        //结构里还可以包含函数
        public StudentStruct(string name, int age, string hobby, int populraity)
        { 
            this.name=name;
            this.age=age;
            this.hobby = hobby;
            this.populraity = populraity;
        }

        public void SayHi()
        {
            Console.WriteLine("姓名:{0},年龄:{1},爱好:{2},受欢迎度:{3}", name, age, hobby, populraity);    
        } 
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            //不用new方式创建！
            StudentStruct ss1;
            ss1.name = "张俊杰";
            ss1.age = 18;
            ss1.hobby = "唱唱歌";
            ss1.populraity = 110;
            ss1.SayHi();

            StudentStruct ss2 = new StudentStruct("周杰杰", 25, "打打球", 80);
            ss2.SayHi();
            Console.ReadKey();
        }
    }
}

————————————————————————————————————————————————————

案例6.1 值类型和引用类型

namespace e6
{
    struct StudentStruct
    {
        public string Name;
        public int Age;
        public string hobby;

 

    }
}

————————————————————————————————————————————————————

案例6.2 

namespace e6
{
    class Student
    {

        public string Name;
        public int Age;
        public string hobby;
    }
}


————————————————————————————————————————————————

案例6.3 

namespace e6
{
    class Program
    {
        static void Main(string[] args)
        {
            //值类型
            /*结构(struct)是值类型，所以它会以传值的方法进行传递
             * 以下例子，把ss1对象赋值给ss2对象，实际上是把结构ss1对象成员如:age
             * 将它的值复制了一份给ss2对象的age，相互之间无任何关系，所以即使改变了
             * ss2对象的值，ss1对象的值也不会发生改变
             * */
            StudentStruct ss1 = new StudentStruct();
            ss1.Age=18;

            StudentStruct ss2=ss1;
            ss2.Age=20;

            Console.WriteLine("ss1结构对象的age:{0},ss2结构对象的age:{1}", ss1.Age, ss2.Age);
            Console.WriteLine();
           
            //----------------------------------------------------------------------------------------------------
            //类 (class)是引用类型，它将会以传引用的方式进行传递
            //以下例子将stu1对象赋给了stu2,实际上传递的是一个引用,即：
            //stu1.age 和stu2.age引用的是同一个内存空间的值,所以
            //stu2.age的值发生改变，两个对象的age都发生了改变
            Student stu1 = new Student();
            stu1.Age = 18;
            Student stu2 = stu1;
            stu2.Age = 20;
            Console.WriteLine("类");
            Console.WriteLine("stu1结构对象的age:{0},stu2结构对象的age:{1}", stu1.Age, stu2.Age);

            Console.ReadKey();
        }
    }
}

——————————————————————————————————————————————————————————————————————————————————————————————————————————————————

案例7 判断 早上好 下午好

namespace l1
{
    public enum TimeOfDay
    { 
        morning=1,
        afternoon,
        evening
    }

 

    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("请输入1. morning, 2.afternoon,3.evening");
            int a = int.Parse(Console.ReadLine());
       

            TimeOfDay time = (TimeOfDay)a;
            switch (time)
            {
                case TimeOfDay.afternoon: Console.WriteLine("Good Afternoon！"); break;
                case TimeOfDay.evening: Console.WriteLine("Good Evening！"); break;
                case TimeOfDay.morning: Console.WriteLine("Good Morning！"); break;
                default: Console.WriteLine("输入错误....."); break;


            }

            Console.ReadKey();
        }
    }
}

————————————————————————————————————————————————————

案例8结构例子

namespace l2
{
    public struct TeacherStruct
    {
        public string teacherName;
        public int teacherAge;
        public int yearsOfService;


        //public TeacherStruct(string teacherName, int teacherAge, int yearsOfService)
        //{
        //    this.teacherName = teacherName;
        //    this.teacherAge = teacherAge;
        //    this.yearsOfService = yearsOfService;

        //}

        public void SayHi()
        {
            Console.WriteLine("大家好，我是{0}老师。我已经在教育战线奋斗了{1}年了", teacherName, yearsOfService);

        }

    }

 


    class Program
    {
        static void Main(string[] args)
        {
            TeacherStruct ts;
            ts.teacherName = "张鬼";
            ts.teacherAge = 35;
            ts.yearsOfService = 15;
            ts.SayHi();


            Console.ReadKey();
        }
    }
}