变量

值类型

枚举

 //枚举a
 enumt emumt2 = enumt.OK;
 //获取枚举变量的值
 int val = (int)emumt2;
 //
    int o = 1;
 //获取枚举名称
 string oname = Enum.GetName(typeof(enumt),o);
 //根据值获取枚举对象
 enumt otype= (enumt)Enum.Parse(typeof(enumt), o.ToString());
 //根据枚举名称获取枚举对象
 enumt otype2 = (enumt)Enum.Parse(typeof(enumt), oname);
 //获取枚举名称数组
 string[] names = Enum.GetNames(typeof(enumt));
 //获取枚举值数组
 var values = Enum.GetValues(typeof(enumt));

结构体

public struct Student
        {
            public int id;
            public string name;
            public int age;
            public void GetStudent()
            {
                Console.WriteLine("id=" + id+",name=?"+name+",age="+age);
            }
            public Student(int id, string name, int age)
            {
                this.id = id;
                this.name = name;
                this.age = age;

            }
        }

static void Main(string[] args)
{
    
    //结构体对象
    //无参构造
    Student student = new Student();
    student.id = 2;
    student.name = "xiaoli";
    student.age = 12;
    student.GetStudent();
    //带参构造
    Student student1 = new Student(3,"XIAOZHAO",21);
    student1.GetStudent();
  }

引用类型

 //引用类型不存储数据值，存储引用
 //1个变量改变内存值 都变
 //string Dynamic Object 
 int value2 = 123;
 object ol = value2;//装箱
 int intol = (int)ol;//拆箱 
 //Dynamic 可存储任何类型
 //程序运行时进行类型检查，和对象类型不同
 dynamic na = "ss";
 dynamic num1 = 222;
 dynamic ll = false;
 //string 
 string na1 = "ss";
 string path = "d:\\document\\imgs";
 string path1 = @"d:\document\imgs";
 //null 空引用
 //null 与 ""区别 ""会分配存储空间，长度为0 而null不会。
  //""等价于 string.Empty 修正 实际值一样

隐式转换

//隐式类型转换 从小变大 从派生类到基类，数据不丢失

           
            //隐式类型转换 从小变大 从派生类到基类
            short shortnum=23;
            int intnum = shortnum;
            long longnum = intnum;
            float floatnum = 3.6f;
            double doublenum = floatnum;
            float floatnum2 = intnum;
            double doublenum2 = intnum;
            decimal decnum = longnum;

// decimal decnum=doublenum /double/float类型不能隐式转换为decimal
decimal decnum = doublenum;

显式转换

type(num)

 //显式类型转换
 //强转 大转小 浮点转整 字符串转值 可能数据丢失
 double doublenumq = 3.56;
 int intnumq = (int)doublenumq;

type.Parse(string)字符串类型转换为值类型

        //type.Parse(string)
        string stringnum = "222.2";
        float floatnumq = float.Parse(stringnum);
        string stringDec = "222.32";
        decimal decimalnum = decimal.Parse(stringDec);
    }
}

c#的值类型
引用类型：C# 中内置的引用类型包括 Object（对象）、Dynamic（动态）和 string（字符串）。

 //
 string str = "22.31";
 int intnum3 = 0;
 bool result = int.TryParse(str, out intnum3);
 string strnum = "32.3";
 result = float.TryParse(strnum, out float floatnums);

            //无法转换也不报错 type.TryParse(string,out type变量)
            string str = "22.31";
            int intnum3 = 0;
            //小数无法转换为int
            bool result = int.TryParse(str, out intnum3);//无法转换
            //如果成功，转换成功str 失败 false
            string strnum = "32.3";
            result = float.TryParse(strnum, out float floatnums);
            //convert.ToType(value) 一种类型转换为指定类型
            object oNum = 120;
            byte byteNum = Convert.ToByte(oNum);
            string strNum = "23123";
            int intNum = Convert.ToInt32(strNum);
            bool boolValue = false;
            string stringBoval = boolValue.ToString();
            double doubleV = 322.21;
            float floatV = Convert.ToSingle(doubleV);  
         }
    }
}

运算符

算数运算符

  //算数运算符
  int a = 30,b = 15;
  int c = a + b;
  int d = a - b;
  int e = a * b;
  int f = a / b;
  int g = a % b;
  int a1 = a++;
  int b2 = --b;
  Console.WriteLine($"a={a},b={b},c={c},d={d},e={e},f={f},g={g},a1={a1},b2={b2}"); 

关系运算符

== >= <= < > !=

            int ax=15,bx=2;
            bool sx = ax == bx;
            bool sx2 = ax != bx;
            bool sx3 = ax > bx;
            bool sx4 = ax < bx;
            bool sx5 = ax >= bx;
            Console.WriteLine($"sx={sx},sx2={sx2},sx3={sx3},sx4={sx4},sx5={sx5}");

逻辑运算符

&& || !

int al = 12, bl = 2, cl = 23, dl = 32;
bool rel1 = al > bl;
bool rel2 = al < bl;
bool rel3 = rel1 && rel2;
bool rel4 = cl >= dl;
bool rel5 = rel4 || rel3;
Console.WriteLine($"rel1={rel1},rel2={rel2},rel3={rel3},rel4={rel4},rel5={rel5}");

位运算符

| & ~ ^

赋值运算符

            //赋值运算符
            int af = 30;
            int bf = 10;
            bf += af;
            Console.WriteLine($"bf={bf}");
            bf -= 6;
            Console.WriteLine($"bf={bf}");
            bf *= 2;
            Console.WriteLine($"bf={bf}");
            bf /= 2;
            Console.WriteLine($"bf={bf}");
            bf %= 10;
            Console.WriteLine($"af={af},bf={bf}");
            int cf = 4;
            //100 
            cf <<= 1;
            //1000=8
            Console.WriteLine(cf);

            cf >>= 1;

            int df = 5;
            df &= 2;
            //5=101 2=010
            //101 & 020 =000
            Console.WriteLine($"cf={cf},df={df}");

            int ef = 6;
            ef ^= 4;
            // ef=110 4=100
            //110 ^ 100=010;2 按位异或 相同为0 不同为1
            Console.WriteLine($"ef={ef}");
            int ff = 31;
            ff |= 32;
            //ff 10000-1=01111
            //32 10000
            //01111 | 10000 = 11111=63
            Console.WriteLine($"ff={ff}");
            
        }
    }

其他运算符

sizeof

 int intSize = sizeof(int);
 int floatSize = sizeof(float);
 int decimalSize = sizeof(decimal);
 int enumSize = sizeof(enumt);
 int charSize = sizeof(char);
 Console.WriteLine($"intsize={intSize},floatS={floatSize}," +
     $"decimalS={decimalSize},enumS={enumSize},charS={charSize}");

typeof

//typeof
Type typeInt=typeof(int);
Type typeStri=typeof(string);
 Type typefloat=typeof(float);
    Type typeDecimal=typeof(decimal);
    Type typeEnum=typeof(enumt);
    Type types = typeof(Student);
    Console.WriteLine("typeint:" + typeInt + ",typestr:" + typeStri+",typefloat:"+typefloat+",typeDe:"+typeDecimal
        +"typeEnum:"+typeEnum+"typestudent:"+types);

条件?A:B

//?:三目运算符
int asan = 21;
string peopleAge = asan < 18 ? "child" : "adult";
Console.WriteLine("people:" + peopleAge);

is

 //is 
 object ai = 22;
 bool si = ai is int;
 Console.WriteLine("ai=?int:"+si);

as

//int intobj=(int)obj;  // 错误：字符串不能直接强制转换为int
//int intobj2 = obj as int;  // 错误：as运算符不能用于值类型

运算符优先级

  int ay = 5;
  int by = 4, cy = 6;
  int dy = ay + by * cy;
  //dy=5+4*6=5+24=29;
  int ey = by > cy ? 1 : 0;
  //ey=4>6 x =0
  int fy = (ay + by) * cy - dy;
  //fy=9*6-29=26 25
  int gy = ++ay + by * (ay - by);
  //6+4*(1)=10 //6+4*2=14
  bool hy = (ay > by) || (cy > by); 
  //true || true =true
  Console.WriteLine("dy:"+dy+",ey:"+ey+",fy:"+fy+",gy:"+gy+",hy:"+hy);