C# 入门学习教程（二）

86Eric2025-07-09 18:39

文章目录

一、操作符详解

C# 中的操作符是用于执行程序代码运算的符号，它们可以对一个或多个操作数进行操作并返回结果。

1、操作符概览

类别 运算符
基本 x.y f(x) a[x] x++ x-- new typeof default checked unchecked delegate sizeof ->
一元 + - ! ~ ++x --x (T)x await &x *x
乘法 * / %
加减 + -
移位 >> <<
关系和类型检测 < > <= >= is as
相等 == !=
逻辑"与" &
逻辑 XOR ^
逻辑 OR |
条件 AND &&
条件 OR ||
null 合并 ??
条件 ?:
lambda 表达式 = *= /= %= += -= <<= >>= &= ^= |= =>
  • 操作符(Operator )也译为"运算符"
  • 操作符是用来操作数据的，被操作符操作的数据称为操作数( Operand )

2、操作符的本质

  • 操作符的本质是函数(即算法)的"简记法"

    • 假如没有发明"+"、只有Add函数，算式3+4+5将可以写成Add(Add(3,4),5)

    • 假如没有发明"x"、只有Mul函数，那么算式3+4x5将只能写成Add(3,Mul(4,5)),注意优先级

  • 操作符不能脱离与它关联的数据类型

    • 可以说操作符就是与固定数据类型相关联的一套基本算法的简记法
    csharp 复制代码 
    namespace CreateOperator
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 5;
            int y = 4;
            int z = x / y;
            Console.WriteLine(z);

            double x1 = 5;
            double y1 = 4;
            double z1 = x1 / y1;
            Console.WriteLine(z1);
        }
    }
}
    • 示例:为自定义数据类型创建操作符
    csharp 复制代码 
    using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CreateOperator
{
    class Program
    {
        static void Main(string[] args)
        {
            //List<Person> nation = Person.GetMarry(persion1,persion2);
            //foreach( var p in nation){
            //    Console.WriteLine(p.Name);
            //}

            List<Person> nation = persion1 + persion2;
            foreach( var p in nation){
                Console.WriteLine(p.Name);
            }

            
        }
    }

    class Person
    {
        public string Name;

        public static List<Person> operator +(Person p1, Person p2)
        {
            List<Person> people = new List<Person> { };
            people.Add(p1);
            people.Add(p2);

            for (int i = 0; i < 11; i++)
            {
                Person child = new Person();
                child.Name = p1.Name + '&' + p2.Name;
                people.Add(child);
            }

            return people;
        }
    }
}

3、操作符的优先级

  • 操作符的优先级
    • 可以使用圆括号提高被括起来表达式的优先级
    • 圆括号可以嵌套
    • 不像数学里有方括号和花括号，在C#语言里"0"与"0"有专门的用途

4、同级操作符的运算顺序

  • 除了带有赋值功能的操作符，同优先级操作符都是由左向右进行运算
    • 带有赋值功能的操作符的运算顺序是由右向左
    • 与数学运算不同，计算机语言的同优先级运算没有"结合率"
      • 3+4+5只能理解为Add(Add(3,4),5)不能理解为Add(3,Add(4,5))

5、 各类操作符的示例

. 操作符

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //. 操作符
            Form a = new Form();
            a.Text = "my form";
            a.ShowDialog();
        }
    }
}

F(x) 函数调用操作符

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //F(x) 函数调用操作符
            calure cc = new calure();
            int dd = cc.Add(1, 2);
            Console.WriteLine(dd);

			//委托
            Action ee = new Action(cc.print);
            ee();
        }
    }
    
    class calure
    {
        public int Add(int a, int b)
        {
            return a + b;
        }

        public void print()
        {
            Console.WriteLine("Hello");
        }
    }
}

a[x]

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] intarray = new int[10];
            console.writeline(intarray[1]);

            int[] intarray2 = new int[5]{11,22,33,44,55};
            console.writeline(intarray2[3]);

          
            dictionary<string,student> stdob = new dictionary<string,student>();
            for (int i = 0; i < 101; i++)
            {
                student stu = new student();
                stu.name = "学生" + i.tostring();
                stu.score = 100 + i;
                stdob.add(stu.name,stu);
            }

            console.writeline(stdob["学生12"].name +"; "+ stdob["学生11"].score);
        }
    }
    
    class student
    {
        public string Name;
        public int Score;
    }

}

x++ x--

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			int x = 100;
			x++;
			Console.WriteLine(x);
			x--;
			Console.WriteLine(x);
			int y = x++;
			Console.WriteLine(x);
			Console.WriteLine(y);
		}
    }
}

typeof

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			Type x = typeof(int);
			Console.WriteLine(x.Name);
			Console.WriteLine(x.FullName);
			Console.WriteLine(x.Namespace);
			int a = x.GetMethods().Length;
			Console.WriteLine(a);
			foreach (var item in x.GetMethods())
			{
			    Console.WriteLine(item.Name);
			}
		}
    }
}

default

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			int a = default(int);
			Console.WriteLine(a);
			
			Form a = default(Form);
			Console.WriteLine(a == null);
			
			leved ll = default(leved);
			Console.WriteLine(ll);
			
			leved22 dd = default(leved22);
			Console.WriteLine(dd);
       }

		enum leved
		{
		    mid,
		    low,
		    High
		}
		
		enum leved22
		{
		    mid = 1,
		    low = 2,
		    High = 3,
		    def = 0
		}
    }
}

new

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			Form myForm = new Form();
            myForm.Text = "hello";
            myForm.ShowDialog();

            Form myFormOne = new Form() { Text = "my text" };
            myFormOne.ShowDialog();

 			// var 自动推断类型
            var myTx = new { text = "1234", age = 55 };
            Console.WriteLine(myTx.text);
            Console.WriteLine(myTx.age);
            Console.WriteLine(myTx.GetType().Name);
		}
    }
}

checked uncheckded

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			uint x = uint.MaxValue;
            Console.WriteLine(x);

            string aa = Convert.ToString(x, 2);
            Console.WriteLine(aa);

            //检测
            checked
            {
                try
                {
                    uint y = x + 1;
                    Console.WriteLine(y);
                }
                catch (OverflowException ex)
                {
                    //捕获异常
                    Console.WriteLine("异常");
                }
            }
		}
    }
}

**delegate **

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ddExample
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            this.myClick.Click += myClick_Click;


            //delegate
            this.myClick.Click += delegate (object sender, RoutedEventArgs e)
            {
                this.myTextBox.Text = "1111111111";
            };

           
            this.myClick.Click += (object sender, RoutedEventArgs e)=>
            {
                this.myTextBox.Text = "1111111111";

            };
        }

        void myClick_Click(object sender, RoutedEventArgs e)
        {
            this.myTextBox.Text = "1111111111";

        }
    }
}

sizeof , ->

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
			int x = sizeof(int);
            Console.WriteLine(x);

            int x1 = sizeof(decimal);
            Console.WriteLine(x1);

            unsafe
            {
                //打印自定义数据结构的长度
                int y = sizeof(StudentStr);
                Console.WriteLine(y);


                //箭头操作符，操作内存
                StudentStr stu;
                stu.age = 16;
                stu.score = 100;

                StudentStr* pStu = &stu;
                pStu->score = 99;

                Console.WriteLine(stu.score);
           }
		}
    }
     struct StudentStr
    {
        public int age;
        public long score;
    }
}

+ - 正负

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {

            int x = 100;
            Console.WriteLine(x);
            int y = -100;
            Console.WriteLine(y);
            int z = -(-x);
            Console.WriteLine(z);

            int x1 = int.MinValue;
            int y1 = -x1;
            Console.WriteLine(x1);
            Console.WriteLine(y1);

            //溢出
            int y2 = checked(-x1);
        }
	}
}

~ 求反

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = int.MinValue;
            int y = ~x;
            Console.WriteLine(x);
            Console.WriteLine(y);
            string xstr = Convert.ToString(x, 2).PadLeft(3, '0');
            string ystr = Convert.ToString(y, 2).PadLeft(3, '0');

            Console.WriteLine(xstr);
            Console.WriteLine(ystr);
        }
	}
}

bool

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            bool x = false;
            bool y = x;
            Console.WriteLine(x);
            Console.WriteLine(y);

            StudentTwo tt = new StudentTwo(null);

            Console.WriteLine(tt.Name);
        }
	}
	
	class StudentTwo
    {
        public string Name;

        public StudentTwo(string Name)
        {
            if (!string.IsNullOrEmpty(Name))
            {
                this.Name = Name;
            }
            else
            {
                throw new ArgumentException("name is empty");
            }
           
        }
    }
}

++x --x

csharp 复制代码 
namespace OperatorExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 100;
            int y = ++x;
            Console.WriteLine(x);
            Console.WriteLine(y);
            int x1 = 100;
            int z = x1++;
            Console.WriteLine(z);
        }
	}
}

(T)x 类型转换

  • 隐式(implicit)类型转换

    • 不丢失精度的转换
    • 子类向父类的转换
    • 装箱显式(explicit)类型转换

  • 有可能丢失精度(甚至发生错误)的转换，即cast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示例隐式(implicit)类型转换
    • 不丢失精度的转换
    • 子类向父类的转换
    • 装箱显式(explicit)类型转换

  • 有可能丢失精度(甚至发生错误)的转换，即cast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示例
csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //隐式类型转换
            //不丢失精度的转换
            int x = int.MaxValue;
            long y = x;
            Console.WriteLine(y);

            // 子类向父类进行的隐式转换
            Teacher t = new Teacher();
            Human h = t;
            h.Eat();
            h.Think();
            Animal a = h;
            a.Eat();

            //显式类型转
            Console.WriteLine(ushort.MaxValue);
            uint x = 65536;
            ushort y = (ushort)x;
            Console.WriteLine(y);
        }

	    class Animal
	    {
	        public void Eat()
	        {
	            Console.WriteLine("Eating....");
	        }
	    }
	
	    class Human : Animal
	    {
	        public void Think()
	        {
	            Console.WriteLine("Think ...");
	        }
	    }
	
	    class Teacher : Human
	    {
	        public void Teach()
	        {
	            Console.WriteLine("Teacher");
	        }
	    }
	}
}
csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace ConertExample
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void button_1_Click(object sender, RoutedEventArgs e)
        {
            double x = System.Convert.ToDouble(TextBox_1.Text);
            double y = System.Convert.ToDouble(TextBox_2.Text);
            double z = x + y;

            //TextBox_3.Text = System.Convert.ToString(z);
            TextBox_3.Text = z.ToString();


            double x1 = double.Parse(TextBox_1.Text);
            double y1 = double.Parse(TextBox_2.Text);
            double z1 = x1 + y1;

            //TextBox_3.Text = System.Convert.ToString(z);
            TextBox_3.Text = z1.ToString();

        }
    }
}
csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace C0onvertExplameT
{
    class Program
    {
        static void Main(string[] args)
        {
            stone ss = new stone();
            ss.Age = 10;

            //explicit
            Monkey mm = (Monkey)ss;

            //implicit
            Monkey mm = ss;

            Console.WriteLine(mm.Age);
        }
    }

    class stone
    {
        public int Age;

        //显式类型转换操作符 explicit 
        public static explicit operator Monkey(stone s)
        {
            Monkey aa = new Monkey();
            aa.Age = s.Age * 100;

            return aa;
        }

        //隐式类型转换  implicit
        //public static implicit operator Monkey(stone s)
        //{
        //    Monkey aa = new Monkey();
        //    aa.Age = s.Age * 200;

        //    return aa;
        //}
    }

    class Monkey
    {
        public int Age;
    }
}

is as

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            // is运算符
            Teacher t = new Teacher();
            var res = t is Teacher;
            Console.WriteLine(res);
            Console.WriteLine(res.GetType().FullName);

            var res1 = t is Human;
            Console.WriteLine(res1);

            var res2 = t is object;
            Console.WriteLine(res2);

            // as 运算符
            object t = new Teacher();
            Teacher tt = t as Teacher;
            if (tt != null)
            {
                tt.Teach();
            }
        }

	    class Animal
	    {
	        public void Eat()
	        {
	            Console.WriteLine("Eating....");
	        }
	    }
	
	    class Human : Animal
	    {
	        public void Think()
	        {
	            Console.WriteLine("Think ...");
	        }
	    }
	
	    class Teacher : Human
	    {
	        public void Teach()
	        {
	            Console.WriteLine("Teacher");
	        }
	    }
	}
}

乘

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 5;
            int y = 6;
            console.writeline(x * y);

            double a = 5.0;
            double b = 4.0;
            var z = a * b;
            console.writeline(z);
            console.writeline(z.gettype().name);

            int a = 5;
            double b = a;
            console.writeline(b.gettype().name);

            int x1 = 5;
            double y1 = 2.5;
            console.writeline(x1 * y1);
            var z = x1 * y1;
            console.writeline(z.gettype().name);
        }
	}
}

除

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 5;
            int y = 4;
            Console.WriteLine(x / y);

            double x1 = 5.0;
            double y1 = 4.0;
            Console.WriteLine(x1 / y1);

            double a = double.PositiveInfinity;
            double b = double.NegativeInfinity;
            Console.WriteLine(a / b);

            double c = (double)5 / 4;
            Console.WriteLine(c);

            double d = (double)(5 / 4);
            Console.WriteLine(d);
        }
	}
}

取余 %

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 0; i < 100; i++)
            {
                Console.WriteLine(i % 10);
            }

            double x = 3.5;
            double y = 3;
            Console.WriteLine(x % y);   
        }
	}
}

加法 + ,减法 -

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //加法 +
            int x = 5;
            double y = 1.5;
            console.writeline(x + y);
            console.writeline((x + y).gettype().name);

            string a = "123";
            string b = "abc";
            console.writeline(a + b);

            //减法 -
            int x = 10;
            double y = 5.0;
            var z = x - y;
            Console.WriteLine(z);
            Console.WriteLine(z.GetType().Name);   
        }
	}
}

位移 >> <<

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //位移，左移一位即原值*2
            int x = 7;
            int y = x << 2;
            Console.WriteLine(y);
            string xStr = Convert.ToString(x, 2).PadLeft(32, '0');
            Console.WriteLine(xStr);
            string yStr = Convert.ToString(y, 2).PadLeft(32, '0');
            Console.WriteLine(yStr);

            //右移一位即原值/2
            int x = 100;
            int y = x >> 2;
            Console.WriteLine(y);
            string xStr = Convert.ToString(x, 2).PadLeft(32, '0');
            Console.WriteLine(xStr);
            string yStr = Convert.ToString(y, 2).PadLeft(32, '0');
            Console.WriteLine(yStr);

            //一直位移的情况下，会出现类型溢出的情况，需要checked

        }
	}
}

**比较运算符 <> == != **

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
           int a = 10;
            int b = 5;
            var c = a < b;
            Console.WriteLine(c);
            Console.WriteLine(c.GetType().FullName);

            char 类型比较大小，转换成ushort 比较大小
            char a = 'a';
            char b = 'A';
            var res = a > b;
            Console.WriteLine(res);
            ushort au = (ushort)a;
            ushort bu = (ushort)b;
            Console.WriteLine(au);
            Console.WriteLine(bu);

            //对齐后，挨个比较unicode
            string str1 = "abc";
            string str2 = "Abc";
            Console.WriteLine(str1.ToLower() == str2.ToLower());

        }
	}
}

**逻辑"与"& ; 逻辑XOR ^ ; 逻辑 OR | **

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 7;
            int y = 10;

            // 按位求与，二进制1为真，0为假，真假为假，真真为真，假假为假
            int z = x & y;
            Console.WriteLine(z);
            string xStr = Convert.ToString(x,2).PadLeft(32,'0');
            string yStr = Convert.ToString(y,2).PadLeft(32,'0');
            string zStr = Convert.ToString(z,2).PadLeft(32,'0');
            Console.WriteLine(xStr);
            Console.WriteLine(yStr);
            Console.WriteLine(zStr);

            // 按位求或，二进制1为真，0为假，真假为真，真真为真，假假为假
            int z = x | y;
            Console.WriteLine(z);
            string xStr = Convert.ToString(x, 2).PadLeft(32, '0');
            string yStr = Convert.ToString(y, 2).PadLeft(32, '0');
            string zStr = Convert.ToString(z, 2).PadLeft(32, '0');
            Console.WriteLine(xStr);
            Console.WriteLine(yStr);
            Console.WriteLine(zStr);

            // 按位求异或，二进制1为真，0为假，不一样为真，一样为假
            int z = x ^ y;
            Console.WriteLine(z);
            string xStr = Convert.ToString(x, 2).PadLeft(32, '0');
            string yStr = Convert.ToString(y, 2).PadLeft(32, '0');
            string zStr = Convert.ToString(z, 2).PadLeft(32, '0');
            Console.WriteLine(xStr);
            Console.WriteLine(yStr);
            Console.WriteLine(zStr);

        }
	}
}

条件与 && 条件或 ||

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 10;
            int y = 5;

            double a = 10.5;
            double b = 5;

            if(x>y && a>b){
                Console.WriteLine("真");
            }
            else
            {
                Console.WriteLine("假");
            }

            if (x < y || a > b)
            {
                Console.WriteLine("真");
            }
            else
            {
                Console.WriteLine("假");
            }
        }
	}
}

null合并 ??

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int? x = null;
            //x = 100;
            Console.WriteLine(x);
            Console.WriteLine(x.Value);

            int y = x ?? 1;
            Console.WriteLine(y);
        }
	}
}

条件 ?:

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int x = 60;
            string str = x >= 60 ? "及格" : "不及格 ";
            Console.WriteLine(str);
        }
	}
}

**赋值 *= += -= /= %= <<= >>= &= ^= |= **

csharp 复制代码 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConversionExample
{
    class Program
    {
        static void Main(string[] args)
        {
            int a = 100;
            int b = a += 10;
            Console.WriteLine(b);

            int c = a>>=1;
            Console.WriteLine(c);
        }
	}
}

二、表达式，语句详解

1. 表达式的定义

  • 什么是表达式

    在 C# 里，表达式是由操作数和运算符组合而成的代码片段，它能计算出一个值。操作数可以是变量、常量、字面量、方法调用等；运算符则用于指明对操作数进行何种运算。

  • C#语言对表达式的定义

    • 算法逻辑的最基本(最小)单元，表达一定的算法意图
    • 因为操作符有优先级，所以表达式也就有了优先级

2. 各类表达式概览

  • C#语言中表达式的分类

    • A value. Every value has an associated type.任何能得到值的运算(回顾操作符和结果类型)
    • A variable. Every variable has an associated type.
    csharp 复制代码 
    int x = 10;
int y;
y = x;
    • A namespace.
    csharp 复制代码 
    //A namespace
System.Windows.Forms.Form myForm;
    • A type.
    csharp 复制代码 
    // A type
 var t = typeof(Int32);
    • A method group.例如:Console.WriteLine,这是一组方法,重载决策决定具体调用哪一个
    csharp 复制代码 
     //A method group
 Console.WriteLine("Hello");

    Console.WriteLine 有19个方法供使用

    • A null literal.
    csharp 复制代码 
         //A null literal
      Form MyForm = null;
    • An anonymous function.
    csharp 复制代码 
    Action a = delegate () { Console.WriteLine("hello"); };
a();
    • A property access.
    csharp 复制代码 
       // a propety access
    Form my = new Form();
    my.Text = "my Text";
    my.ShowDialog();
    • An event access.
    csharp 复制代码 
    static void Main(string[] args)
{
 Form myFo = new Form();
 myFo.Load += myFo_Load;
 myFo.ShowDialog();
}

static void myFo_Load(object sender, EventArgs e)
{
    Form form = sender as Form;
    if (form == null)
    {
        return;
    }

    form.Text = "new Text";
}
    • An indexer access.
    csharp 复制代码 
     List<int> listone = new List<int> { 1, 22, 333 };
 int xOne = listone[2];
    • Nothing.对返回值为void的方法的调用
    csharp 复制代码 
     //Nothing
 Console.WriteLine("Hello");
  • 复合表达式的求值
    • 注意操作符的优先级和同优先级操作符的运算方向

3. 语句的定义

  • Wikipedia对语句的定义

    语句是高级语言的语法

    编译语言和机器语言只有指令(高级语言中的表达式对应低级语言中的指令)，语句等价于一个或一组有明显逻辑关联的指令。

  • C#语言对语句的定义

    • C#语言的语句除了能够让程序员"顺序地"(sequentially)表达算法思想，还能通过条件判断、跳转和循环等方法控制程序逻辑的走向
    • 简言之就是:陈述算法思想，控制逻辑走向，完成有意义的动作(action)
    • C#语言的语句由分号(;)结尾，但由分号结尾的不一定都是语句
    • 语句一定是出现在方法体里

4. 语句详解

  • 声明语句
csharp 复制代码 
int xSF = 100;
var x1 = 200;
const int xC = 100;
  • 表达式语句
csharp 复制代码 
Console.WriteLine("Hello World");

new Form();

int xT = 100;
xT = 200;

xT++;
xT--;
++xT;
--xT;
  • 块语句
csharp 复制代码 
{
    int XTo = 100;
    if (XTo < 100)
    Console.WriteLine("不及格");
}
  • 标签语句
csharp 复制代码 
 {
 hello: Console.WriteLine("Hello World");
     goto hello;
 }
  • 块语句的作用域
csharp 复制代码 
 int ykuai = 100;
 {
     int xkuai = 200;
     Console.WriteLine(ykuai);
 }
 // 无法在块语句外打印xkuai
 Console.WriteLine(xkuai);
  • if 语句
csharp 复制代码 
 int score = 59;
 if (score >= 80)
 {
     Console.WriteLine("A");
 }
 else if (score >= 60)
 {
     Console.WriteLine("B");
 }
 else if (score >= 40)
 {
     Console.WriteLine("C");
 }
 else
 {
     Console.WriteLine("D");
 }
  • switch 语句
csharp 复制代码 
static void Main(string[] args)
{
  Level myLevel = new Level();
  switch (myLevel)
   {
       case Level.High:
           Console.WriteLine(Level.High);
           break;
       case Level.Mid:
           Console.WriteLine(Level.Mid);
           break;
       case Level.Low:
           Console.WriteLine(Level.Low);
           break;
       default:
           Console.WriteLine("凉凉");
           break;
   }
}
   
enum Level
{
    High,
    Mid,
    Low
}
  • try 语句,尽可能多的去处理异常
csharp 复制代码 
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace ExpressionExample
{
	class Program
	{
		static void Main(string[] args)
		{
			Count cc = new Count();
			int res = cc.Add("122222222", "122222222");
			Console.WriteLine(res);
		}
	}

	class Count
	{
	    public int Add(string a, string b)
	    {
	        int x = 0;
	        int y = 0;
	
	        bool error = false;
	        try
	        {
	            x = int.Parse(a);
	            y = int.Parse(b);
	        }
	        catch (ArgumentNullException ex)
	        {
	            Console.WriteLine(ex.Message);
	            error = true;
	        }
	        catch (FormatException ex)
	        {
	            Console.WriteLine(ex.Message);
	            error = true;
	        }
	        catch (OverflowException ex)
	        {
	            Console.WriteLine(ex.Message);
	            error = true;
	        }
	        finally
	        {
	            if (error)
	            {
	                Console.WriteLine("有错误不能计算");
	            }
	            else
	            {
	                Console.WriteLine("一切正常");
	            }
	
	        }
	
	        int z = x + y;
	
	        return z;
	
	    }
	}
}
  • while 循环语句
csharp 复制代码 
namespace ExpressionExample
{
	class Program
	{
		static void Main(string[] args)
		{
			 bool next = true;
			 while (next)
			 {
			     Console.WriteLine("请输入数字1：");
			     string str1 = Console.ReadLine();
			     int a1 = int.Parse(str1);
			
			     Console.WriteLine("请输入数字2：");
			     string str2 = Console.ReadLine();
			     int a2 = int.Parse(str2);
			
			     if (a1 + a2 == 100)
			     {
			         next = false;
			         Console.WriteLine("已经 100");
			     }
			     else
			     {
			         Console.WriteLine("请继续");
			     }
			 }
		 }
 	}
}
  • do while 循环语句
csharp 复制代码 
namespace ExpressionExample
{
	class Program
	{
		static void Main(string[] args)
		{
			bool nextDo = false;
            do
            {
                Console.WriteLine("请输入数字1：");
                string str1 = Console.ReadLine();
                int a1 = 0;
                try
                {
                    a1 = int.Parse(str1);
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                    continue;
                }

                Console.WriteLine("请输入数字2：");
                string str2 = Console.ReadLine();
                int a2 = 0;
                try
                {
                    a2 = int.Parse(str2);
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                    continue;
                }

                if (a1 == 100 || a2 == 100)
                {
                    Console.WriteLine("100 直接退出");
                    break;
                }

                if (a1 + a2 == 100)
                {
                    nextDo = false;
                    Console.WriteLine("已经 100");
                }
                else
                {
                    nextDo = true;
                    Console.WriteLine("请继续");
                }
            } while (nextDo);
		 }
 	}
}
  • for 循环语句，99乘法表
csharp 复制代码 
namespace ExpressionExample
{
	class Program
	{
		static void Main(string[] args)
		{
	
			for (int i = 1; i < 10; i++)
            {
                for (int j = 1; j < 10; j++)
                {
                    if (i >= j)
                    {
                        int z = i * j;
                        Console.Write("{0} * {1} = {2} ", i, j, z);
                    }
                    else
                    {
                        Console.WriteLine("");
                        break;
                    }
                }
            }

		}
 	}
}
  • 迭代器 与 foreach
csharp 复制代码 
namespace ExpressionExample
{
	class Program
	{
		static void Main(string[] args)
		{
			int[] ints = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
			IEnumerator values = ints.GetEnumerator(); //指月
			
			while (values.MoveNext())
			{
			    Console.WriteLine(values.Current);
			}
			
			//重置
			values.Reset();
			while (values.MoveNext())
			{
			    Console.WriteLine(values.Current);
			}
			
			// foreach 语句
			foreach (int i in ints)
			{
			    Console.WriteLine(i);
			}
		}
 	}
}
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