C# 操作符
C# 操作符
- 一、操作符概览
- 二、优先级与运算顺序
- 三、各类操作符的实例
一、操作符概览
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操作符（运算符）的本质是函数的简记法
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操作符不能脱离与它关联的数据类型
int x = 5; int y = 4; int z = x / y; Console.WriteLine(z);//输出1double 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
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按表格顺序从上到下优先级依次降低
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同优先级操作符从左到右
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赋值操作符从右到左
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
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访问外层名称空间的子集名称空间
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访问名称空间的类型
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访问类型的静态成员
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
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访问对象的成员
Form myForm = new Form(); myForm.Text = "Hello, World!"; myForm.ShowDialog();
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f(x)方法调用操作符 -
a[x]元素访问操作符//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int x = 100;int y = x++;Console.WriteLine(x);//101Console.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Form myForm1 = new Form();Form myForm2 = new Form() { Text = "Hello" };//匿名类型var person = new { Name = "Mr.Ok", Age = 34 };Console.WriteLine(person.Name);//Mr.OkConsole.WriteLine(person.Age);//34 -
typeof操作符：查看一个类型的内部结构Type t = typeof(int);Console.WriteLine(t.Namespace);//SystemConsole.WriteLine(t.FullName);//System.Int32Console.WriteLine(t.Name);//Int32int 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//结构体类型int x = default(int);Console.WriteLine(x);//0//引用类型Form myForm = default(Form);Console.WriteLine(myForm == null);//trueclass Program {static void Main(string[] args){//枚举类型Level1 level1 = default(Level1);Console.WriteLine(level1); //LowLevel2 level2 = default(Level2);Console.WriteLine(level2); //MediumLevel3 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//第一种用法uint x = uint.MaxValue;uint y = x+1;Console.WriteLine(x);//4294967295Console.WriteLine(y);//0try{uint z = checked(x + 1);Console.WriteLine(z);}catch (OverflowException ex){Console.WriteLine("There's overflow");//There's overflow}//第二种用法uint x = uint.MaxValue;uint y = x + 1;Console.WriteLine(x);//4294967295Console.WriteLine(y);//0checked{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int x = sizeof(int);Console.WriteLine(x);//4class 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。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; } -
*xclass 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1int x = int.MinValue;int y = -x;Console.WriteLine(x)//-2147483648Console.WriteLine(y);//-2147483648string xStr = Convert.ToString(x,2).PadLeft(32,'0');//10000000000000000000000000000000string yStr = Convert.ToString(y, 2).PadLeft(32, '0');//10000000000000000000000000000000Console.WriteLine(xStr);Console.WriteLine(yStr); -
(T)x：强制类型转换操作符- 隐式类型转换
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不丢失精度的转换
//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
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装箱
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- 显式类型转换
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有可能丢失精度（甚至发生错误）的转换，即cast
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
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使用Convert类
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ToString方法与各数据类型的Parse/TryParse方法
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- 自定义类型转换操作符
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; } - 隐式类型转换
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/：除法操作符
int x1 = 5;int y1 = 4;Console.WriteLine(x1 / y1);//1double x2 = 5.0;double y2 = 4.0;Console.WriteLine(x2 / y2);//1.25
//被除数为0int 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
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);//TrueConsole.WriteLine(result2);//TrueConsole.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
object obj = new Teacher();Teacher t = obj as Teacher;if (t != null){t.Teach();//Teaching...}
&&和||，注意短路效应
int x = 3;int y = 4;int a = 3;if (x > y && a++ > 3){Console.WriteLine("Hello");}Console.WriteLine(a);//3
int x = 5;int y = 4;int a = 3;if (x > y && a++ > 3){Console.WriteLine("Hello");}Console.WriteLine(a);//4
int x = 5;int y = 4;int a = 3;if (x > y || a++ > 3){Console.WriteLine("Hello");//Hello}Console.WriteLine(a);//3
int x = 3;int y = 4;int a = 3;if (x > y || ++a > 3){Console.WriteLine("Hello");//Hello}Console.WriteLine(a);//4