C# 操作符

一、操作符概览

操作符（运算符）的本质是函数的简记法

操作符不能脱离与它关联的数据类型

csharp 复制代码

int x = 5;
int y = 4;
int z = x / y;
Console.WriteLine(z);//输出1

double a = 5.0;
double b = 4.0;
double c = a / b;
Console.WriteLine(c);//输出1.25

二、优先级与运算顺序

按表格顺序从上到下优先级依次降低
同优先级操作符从左到右

赋值操作符从右到左

csharp 复制代码

int x = 100;
int y = 200;
int z = 300;
x += y += z;
Console.WriteLine(x);//600
Console.WriteLine(y);//500
Console.WriteLine(z);//300

三、各类操作符的实例

x.y成员访问操作符

访问外层名称空间的子集名称空间
访问名称空间的类型
访问类型的静态成员
csharp 复制代码
```
System.IO.File.Create("D:\\HelloWorld");
```
- System.IO:外层名称空间的子集名称空间
- IO.File:名称空间的类型
- File.Create:类型的静态成员

访问对象的成员

csharp 复制代码

Form myForm = new Form();
myForm.Text = "Hello, World!";
myForm.ShowDialog();

f(x)方法调用操作符

a[x]元素访问操作符

csharp 复制代码

//访问数组
int[] myArray1 = new int[10];
int[] myArray2 = new int[] { 1,2,3,4,5};
int[] myArray3 = new int[5] { 1, 2, 3, 4, 5 };
Console.WriteLine(myArray2[0]);

//访问字典
class Program
{
	static void Main(string[] args)
	{
  	  Dictionary<string, Student> stuDic = new Dictionary<string, Student>();
  	  
   	  for (int i = 0; i < 100; i++)
   	  {
   	     Student student = new Student();
   	     student.Name = "s_" + i.ToString();
  	     student.Score = i;
     	 stuDic.Add(student.Name, student);
 	   }

      Student number6 = stuDic["s_6"];
      Console.WriteLine(number6.Score);//6
  }

    
}

class Student
{
  public string Name;
  public int Score;
}

x++后置自增，x--后置自减。遇到赋值，先赋值，后自增/自减

csharp 复制代码

        int x = 100;
        int y = x++;
        Console.WriteLine(x);//101
        Console.WriteLine(y);//100

new：在内存中创造一个类的实例，（1）立即调用这个实例的构造器，（2）调用实例的初始化器

csharp 复制代码

        Form myForm1 = new Form();
        Form myForm2 = new Form() { Text = "Hello" };

csharp 复制代码

		//匿名类型
        var person = new { Name = "Mr.Ok", Age = 34 };
        Console.WriteLine(person.Name);//Mr.Ok
        Console.WriteLine(person.Age);//34

typeof操作符：查看一个类型的内部结构

csharp 复制代码

        Type t = typeof(int);
        Console.WriteLine(t.Namespace);//System
        Console.WriteLine(t.FullName);//System.Int32
        Console.WriteLine(t.Name);//Int32
        int c = t.GetMethods().Length;
        foreach (var mi in t.GetMethods())
        {
            Console.WriteLine(mi.Name);//CompareTo、 Equals、GetHashCode ......
        }
        Console.WriteLine(c);//53

default：获取一个类型的默认值

csharp 复制代码

        //结构体类型
        int x = default(int);
        Console.WriteLine(x);//0

csharp 复制代码

        //引用类型
        Form myForm = default(Form);
        Console.WriteLine(myForm == null);//true

csharp 复制代码

class Program
{
    static void Main(string[] args)
    {

        //枚举类型
        Level1 level1 = default(Level1);
        Console.WriteLine(level1); //Low

        Level2 level2 = default(Level2);
        Console.WriteLine(level2); //Medium

        Level3 level3 = default(Level3);
        Console.WriteLine(level3); //逻辑出错，输出0
    }


}
enum Level1
{
    Low,
    Medium,
    High

}
enum Level2
{
    Low = 1,
    Medium = 0,
    High = 2

}

enum Level3
{
    Low = 2,
    Medium = 1,
    High = 3

}

checked/unchecked：检查一个值是否有溢出

csharp 复制代码

		//第一种用法
		uint x = uint.MaxValue;
		uint y = x+1;
		Console.WriteLine(x);//4294967295
		Console.WriteLine(y);//0

		try
		{
		    uint z = checked(x + 1);
		    Console.WriteLine(z);

		}
		catch (OverflowException ex)
		{
			 Console.WriteLine("There's overflow");//There's overflow
		}

csharp 复制代码

		//第二种用法
        uint x = uint.MaxValue;
        uint y = x + 1;
        Console.WriteLine(x);//4294967295
        Console.WriteLine(y);//0

        checked
        {
            try
            {
                uint z = x + 1;
                Console.WriteLine(z);

            }
            catch (OverflowException ex)
            {

                Console.WriteLine("There's overflow");//There's overflow

            }

        }

sizeof: 获取基本类型在内存中占的字节数

csharp 复制代码

        int x = sizeof(int);
        Console.WriteLine(x);//4

csharp 复制代码

class Program
{
    static void Main(string[] args)
    {
        unsafe {
            int y = sizeof(Student);
            Console.WriteLine(y);
        }
    }
}

class Student {
    int ID;
    long Score;
}

->：箭头操作符。会直接操作内存，因此需要放在不安全的上下文使用。只能操作结构体类型。

csharp 复制代码

class Program
{
    static void Main(string[] args)
    {

        unsafe
        {
            Student stu;
            stu.ID = 1;
            stu.Score = 60;
            Student* pStu = &stu;
            pStu->Score = 90;
            Console.WriteLine(stu.Score);//90

        }
    }
}

struct Student
{
    public int ID;
    public long Score;
}

*x

csharp 复制代码

class Program
{
    static void Main(string[] args)
    {

        unsafe
        {
            Student stu;
            stu.ID = 1;
            stu.Score = 60;
            Student* pStu = &stu;
            pStu->Score = 90;
            (*pStu).Score = 1000;
            Console.WriteLine(stu.Score);//100

        }
    }
}

struct Student
{
    public int ID;
    public long Score;
}

-x：相反数操作符，在二进制的基础上，按位取反，再加1

csharp 复制代码

 int x = int.MinValue;
 int y = -x;
 Console.WriteLine(x)//-2147483648
 Console.WriteLine(y);//-2147483648
 string xStr = Convert.ToString(x,2).PadLeft(32,'0');//10000000000000000000000000000000
 string yStr = Convert.ToString(y, 2).PadLeft(32, '0');//10000000000000000000000000000000
 Console.WriteLine(xStr);
 Console.WriteLine(yStr);

(T)x：强制类型转换操作符

隐式类型转换

不丢失精度的转换

csharp 复制代码

//短整型转换成长整型
int x = int.MaxValue;
long y = x;
Console.WriteLine(y);

源	目标
sbyte	short、int、long、float、double 或 decimal
byte	short、ushort、int、uint、long、ulong、float、double 或 decimal
short	int、long、float、double 或 decimal
ushort	int、uint、long、ulong、float、double 或 decimal
int	long、float、double 或 decimal
uint	long、ulong、float、double 或 decimal
long	float、double 或 decimal
char	ushort、int、uint、long、ulong、float、double 或 decimal
float	double
ulong	float、double 或 decimal

子类向父类的转换
装箱

显式类型转换

有可能丢失精度（甚至发生错误）的转换，即cast

csharp 复制代码

int x = 100;
short y = (short)x;
Console.WriteLine(y);

源	目标
sbyte	byte、ushort、uint、ulong 或 char
byte	Sbyte 或 char
short	sbyte、byte、ushort、uint、ulong 或 char
ushort	sbyte、byte、short 或 char
int	sbyte、byte、short、ushort、uint、ulong 或 char
uint	sbyte、byte、short、ushort、int 或 char
long	sbyte、byte、short、ushort、int、uint、ulong 或 char
ulong	sbyte、byte、short、ushort、int、uint、long 或 char
char	sbyte、byte 或 short
float	sbyte、byte、short、ushort、int、uint、long、ulong、char 或 decimal
double	sbyte、byte、short、ushort、int、uint、long、ulong、char、float 或 decimal
decimal	sbyte、byte、short、ushort、int、uint、long、ulong、char、float 或 double

拆箱
使用Convert类
ToString方法与各数据类型的Parse/TryParse方法

自定义类型转换操作符

csharp 复制代码

class Program
{
    static void Main(string[] args)
    {
          Stone stone = new Stone();
          stone.Age = 5000;
          Monkey wukong = (Monkey)stone;
          Console.WriteLine(wukong.Age);//10
    }
}


class Stone
{
    public int Age;
    public static explicit operator Monkey(Stone stone)
    {
        Monkey m = new Monkey();
        m.Age = stone.Age / 500;
        return m;
    }
}
class Monkey
{
    public int Age;
}

/：除法操作符

csharp 复制代码

            int x1 = 5;
            int y1 = 4;
            Console.WriteLine(x1 / y1);//1
            double x2 = 5.0;
            double y2 = 4.0;
            Console.WriteLine(x2 / y2);//1.25

csharp 复制代码

            //被除数为0
            int x1 = 5;
            int y1 = 0;
            Console.WriteLine(x1 / y1);//报错

            double x2 = 5.0;
            double y2 = 0;
            Console.WriteLine(x2 / y2);//∞

is：检验一个对象是不是某个类型的对象

csharp 复制代码

    class Program
    {
        static void Main(string[] args)
        {
            Teacher t1 = new Teacher();
            Teacher t2 = null;

            var result1 = t1 is Teacher;
            var result2 = t1 is Hunam;
            var result3 = t2 is Teacher;
    
            Console.WriteLine(result1);//True
            Console.WriteLine(result2);//True
            Console.WriteLine(result3);//False

        }
    }


    class Animal {
        public void Eat() {
            Console.WriteLine("Eating...");
        }
    }

    class Hunam:Animal
    {
        public void Think()
        {
            Console.WriteLine("Thinking...");
        }
    }

    class Teacher : Hunam
    {
        public void Teach()
        {
            Console.WriteLine("Teaching...");
        }
    }

as

csharp 复制代码

   object obj = new Teacher();
   Teacher t = obj as Teacher;
   if (t != null)
     {
         t.Teach();//Teaching...
     }

&&和||，注意短路效应

csharp 复制代码

            int x = 3;
            int y = 4;
            int a = 3;
            if (x > y && a++ > 3)
            {
                Console.WriteLine("Hello");
            }
            Console.WriteLine(a);//3

csharp 复制代码

            int x = 5;
            int y = 4;
            int a = 3;
            if (x > y && a++ > 3)
            {
                Console.WriteLine("Hello");
            }
            Console.WriteLine(a);//4

csharp 复制代码

            int x = 5;
            int y = 4;
            int a = 3;
            if (x > y || a++ > 3)
            {
                Console.WriteLine("Hello");//Hello
            }
            Console.WriteLine(a);//3

csharp 复制代码

            int x = 3;
            int y = 4;
            int a = 3;
            if (x > y || ++a > 3)
            {
                Console.WriteLine("Hello");//Hello
            }
            Console.WriteLine(a);//4