C# basic knowledge compilation: C# basics (1)

C#Basic structure

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class MyFirstClass
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello world!");

            Console.ReadLine();
        }
    }
}

(1), variable definition
;
Example, MyFirstClass myFirstClass ;
(2), how to initialize variables
int a = 0;
string str=string.Empty;
int init = a*2;
(3). Scope of variables
First of all, you should clarify the respective scopes of private, protected, internal and public.
private-completely private, can only be called in this class, and cannot be called in subclasses or other classes. When inheriting, subclasses cannot inherit private properties or methods.
protected-Same as private, but the difference is that subclasses in protected can access and inherit members and methods.
internal-Public, can be accessed in the same assembly, but not in other assemblies.
public-Completely public, it can be accessed as long as it is in a project. However, if it is a different assembly, it needs to reference the assembly in which it is located.
Then the scope of variables declared by these types is the same as their scope;
The scope of general variables is as follows:
a. The class to which the variable belongs is in a certain scope, and the attributes or methods are also in a certain scope. in scope.
b. The scope of local variables, before the braces that end the block statement or method in which the variable is declared.
(4), Constant
When declaring a variable, add the const keyword in front of the variable to specify the variable as a constant.
Note:
　a constant must be initialized when declared, and it cannot be changed after its value is assigned.
　b Constants are always static, and there is no need to add the static keyword when declaring constants.
(5) String processing
String processing should be used more often. The commonly used as follows:

string testString = @"Hello,world!";
            testString.Substring(0, 1);
            testString.Trim();
            testString.TrimEnd('\n');
            testString.TrimStart('0');

and there are also all, contains, startwith, endwith, etc. In vs, you can see all methods and attributes.
(6) Use regular expressions
Regular expressions are widely used in projects. Please refer to the following articles:
Regular character description: http://www.php.cn /;
Commonly used regular rules: http://www.php.cn/.
(7). What is CTS type?
A given assembly may contain any number of different "types". In the .NET field, type is a general term that refers to any member of the collection {class, interface, structure, enumeration, delegate}. When building solutions in .NET-enabled languages, you'll most likely have to deal with these types. For example, an assembly might define a class that implements some interfaces. Perhaps one of the interface methods takes an enumeration type as an input parameter and returns a structure when called.

CTS (Common Type System) is a formal specification that specifies how types must be defined in order to be carried by the CLR. Typically, only those creating tools or compilers targeting the .NET platform care much about the inner workings of CTS. However, it is important for all .NET programmers to learn how to use the five types defined by CTS in the language they use. Here is a brief summary.
Every language that supports .NET must at least support the concept of class type, which is the basis of object-oriented programming (OOP). A class may consist of many members (such as properties, methods, and events) and data (fields). In C#, use the class keyword to declare a class:

// C#类类型。
class Calc
{
    public int Add(int x, int y)
    { 
        return x + y; 
    }
}

Table CTS class type

Whether the class is concrete or abstractVisibility must be set for each class. Basically, visibility defines whether the class is used by an external assembly or can only be used in the assembly in which it is defined

Characteristics of classes	Meaning in the life cycle
Whether the class is "sealed"	Sealed classes cannot be used as base classes for other classes
Does the class implement any interfaces	An interface is a collection of abstract members that provides a contract between an object and its users. CTS allows a class or structure to implement any number of interfaces
Abstract classes cannot be created directly, but they can be used to define public behaviors for derived types. Concrete classes can be created directly	#What is the visibility of this class
	（8) 数据类型如何分类以及各个数据类型范围？ http://www.php.cn/ （9）操作符 括号操作符 格式() 点操作符 格式 (E.I) 其中E是基本表达式或者预定义类型，I是一个标识符。C++里除了"."之外还有"::" "->"，C#里用点操作符来代替。比如一个类T有成员变量M，在C++里用T::M来引用，C#里用T。M来引用。另一点不同的是，C#里预定义类型也是从Object类派生出来的，因此也定义了成员变量，比如，I是一个short类型的变量，那么I。ToInt()操作将返回一个Int类型的值。 后缀加减操作符 格式:p++;p--; ++p; --p; 结果是给变量p加1或减1 new操作符 格式:a， new 类型(参数列表) b，new 数组类型初始化列表 c，new 代表类型(表达式) typeof操作符 该操作返回一个类型对应的system。type，如: typeof(int); typeof(System。Int32); typeof(string); 各自的结果为int32，int32，string。typeof只对类型操作，不能对变 量操作，例如，"int I;typeof(I);"是不合法的 sizeof操作符 该操作可获得一个类型所占用的空间大小，以字节为单 位。该操作符用在unsafe模块中，如 Unsafe{ S=sizeof(int); } 或者在调用该操作符的函数中使用该前缀。 单目操作符 (1)+-操作 (2)逻辑非:!(表达式) (3)位非:～(表达式) (4)强制类型转换: (T) 表达式 关系运算符 ==，!=，，=， is is用来判断一个变量是否是某一类型，例如，s is string 位逻辑操作符 &(位与)，|(位或)，^(异或)。可以对整数，布尔，和枚 举类型进行这三种操作。 条件逻辑操作符 包括&&(与)和||(或) 条件运算符 b x:y b为真，结果是x，否则是y 以上就是C#基础知识整理：C#基础（1）的内容，更多相关内容请关注PHP中文网（www.php.cn）！