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: //m.sbmmt.com /;
Commonly used regular rules: //m.sbmmt.com/.
(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

typeof(int); typeof(System。Int32); typeof(string);

Unsafe{ S=sizeof(int); }