Detailed introduction to the basic knowledge of C# in ASP.NET

This article mainly introduces the basic knowledge of C# in ASP.NET. It has a certain reference value, let’s take a look with the editor below

Explanation: asp.net as a developmentframework is now widely used, and its development foundation is in addition to the front-end The most important language support for backends such as html, css, JavaScript, etc. is C#. The following is a summary of the main basic knowledge used for future learning.

1. C# is an object-orientedprogramming language, mainly used to develop applications that can run on the .net platform. is a strongly typed language, so every variable must have a declared type. There are two data types in C#: value types and reference types. (Where value types are used to store values, reference types are used to store references to actual data).

1. Value type

The value type represents the actual data and is stored in the stack. Most basic types in C# are numeric types. Value types include simple types, enumeration types, and structure types.

Simple types include numerical types and bool types. (Generally, choose the numeric type according to your needs. When the value is small, you can try to choose the byte type).

2. Reference type

The reference type represents a pointer or reference to data and can store references to actual data. When the reference type is null, it means that no object is referenced. Reference types include interfaces, classes, arrays, pointers, etc. The classes include boxing types, delegates, and custom classes. (Note: Although string is an application type, if the equality operator == or != is used, it means comparing the value of the string object).

3. Boxing and unboxing

Simply put, boxing is the conversion from value type to reference type. Likewise, unboxing is a conversion from a reference type to a value type. Using unboxing, you can operate complex reference types just like simple types, which is also a powerful feature of C#.

Simple examples of boxing and unboxing

class Test
 {
 static void Mian()
 {
  int i = 3;
  object a = i;//装箱
  int j = (int)a;//拆箱
 }
 }

Explanation: During the process of boxing and unboxing, any value type can be viewed as an object reference type. When a boxing operation converts a value type to a reference type, there is no need to explicitly cast the type; while an unboxing operation converts a reference type to a value type, because it can force Convert to any compatible value type, so the type conversion must be done explicitly.

2. Constants and variables

const keyword in front of the type of the field. The constant must be initialized when declaring. Constants can be marked as public, private, protected, internal, protected internal. These access modifiers define how users can access the constant.

variable names should be as meaningful as possible for easy reading. Variables are quantities whose values ​​continuously change during the running of the program. They are usually used to save the data input during the running of the program, the intermediate results obtained by calculations, and the final results.

Modifier access level:

3. Type conversion

1. Implicit type conversion

safely perform the conversion without checking.

Note: Precision loss will occur when converting from int long ulong float simple type to float.

2. Explicit type conversion

Explicit type conversion can also be called forced type conversion, which requires Declare the type to be converted. If you are converting between types for which no implicit conversion exists, you need to use an explicit type conversion.

Forced type conversion can use the Convert keyword to force data type conversion.

For example: float f=123.345;

int i=(int)f;

Or: float f=123.345

int i=Convert. ToInt32(f);

Note: Since explicit type conversion includes all implicit type conversions and explicit type conversions, cast type conversion can always be used at one timeExpressionFrom Converts any numeric type to any other numeric type.

4. Operators and expressions

C# provides a large number of operators, which specify which operations are performed in expressions symbol. An expression is a piece of code that can be evaluated and results in a single value, object, method, or namespace.

1, Arithmetic operators and arithmetic expressions

2. Relational operators and relational expressions

3, Assignment operator and assignment expression

attribute, event, or index element. Commonly used ones include: =, +=, -=, *=, /=, ^=, %=, <<= (right shift assignment), >>= (left shift assignment), etc.

4, Logical operators and logical expressions

5, bit operator

//格式化为Currency类型
string str1=String.Format("(C)Currency:{0:C}\n",-123.4556f);
//格式化为ShortDate类型
string str2=String.Format("(d)ShortDate:{0:d}\n",DateTime.Now);

string str="hello world";
string[] split=str.Split(new Char[]{'.','!'});
foreach(string s in split)
{
 if(s.Tirm()!='''')
 {
 Console.WriteLine(s);
 }
//或者修改为
 string []split=str.Split(','.'!');

String Trim(Char[]);//从字符串的开头和结尾处一处空白。
String TrimStart(Char[]);//从字符串的开头处移除字符串在字符数组中指定的字符。
String TrimEnd(Char[]);//从字符串的结尾处移除字符数组中指定的字符。

//举例
int []arr=new int[6];
int [,]arr=new int[2,3];
int []arr1=new int[3]{1,2,3};
int [,]arr2=new int[3,2]{{2,3},{5,5},{3,5}};
string []arr;
arr=new string[3]{"sd","dddd","aaaa"};
int [,]arr;
arr=new int[,]{{2,3},{4,5},{4,2}};
//创建数组时可以省略new和数组长度
string[]arr={"ddd","fff","sss"};
int [,]arr3={{2,3},{4,5},{3,2}};

int []arr={2,3,6,3,2};
foreach(int i in arr){
 system.Console.write({0},i);
}