A little knowledge of C# (1)

Little knowledge (1)

var:

Initialization must have a value assignment, var i; (wrong).

The type of an object of type var is not allowed to be changed during operation. (For example: var i=1; i="hello!" will cause an error)

var only declares local variables.

dynamic:

No value can be assigned during initialization.

This type can be given to dynamic type objects during operation. (For example: dynamic i=1; i="hello!" No error)

can be declared as a global variable.

VAR and DYNAMIC: Generally used when the variable type is uncertain.

decimal：

High-precision decimal, range: 1.0*10^-28 to 7.9*10^28, precision 28 digits. Generally used to express money. The precision of float/double is 7/15 digits. When using these two types of float/double to represent currency, it will "erase zeros" for you.

Decimal default value: 0.0M

float default value: 0.0F

double default value: 0.0D

char:

char character There are 3 types of assignment:

char c='d';

char c='\x0068'; hexadecimal

char c='\u0068'; Unicode means

char c=(char)68; Integer conversion to char.

Default value: '\x0000'

Octal and hexadecimal:

In C#, integers are only expressed in decimal, using the octal format specifier" o" or "O" and the hexadecimal format specifier is "x" or "X", a compilation error will occur (for example: int i = o73; error).

When you need to output octal or hexadecimal, just use i.ToString("x").

• Display binary WriteLine(Convert.ToString(231,2));

• ## Display octal WriteLine(Convert.ToString( 231,8)) ;

• Display hexadecimal WriteLine(Convert.ToString(231,16));

• Display hexadecimal WriteLine(i.ToString("x")); displays lowercase.

• Display hexadecimal WriteLine(i.ToString("X")); display uppercase.

PadLeft and PadRight

The left or right side of the output string is filled with spaces to achieve right or left alignment.

ToString().PadLeft(8); The output string length is 8, with spaces on the left.

Parse:

Parse parsing, converts the string representation of a number into an equivalent number.

Such as: int.parse(string); double.parse(string); decimal.parse(string) and so on.

There is no parse method for var and dycimal.

Note: When converting a string of hexadecimal numbers to int, use the Parse(string,System.Globalization.NumberStyle) method, and select HexNumber for the second enumeration parameter.

How to parse binary strings and octal strings into int? I don’t know yet... Can any master tell me? ? ?

Encoding:

Conversion between string and byte array. System.Text.Encoding class

byte[] ← GetBytes(string) method, converts a string into a byte array.

String ← GetString(byte[]) method converts a byte array into a string.

Encoding attribute:

• Encoding.Default Gets the encoding of the system’s current ANSI code page

• Encoding.UTF7 Gets UTF7 Encoding format

## Encoding.UTF8 Gets the UTF8 encoding format
Encoding.ASCII Gets the encoding of the 7-bit ASCII character set
Encoding.Unicode Gets the encoding of a specific sequence of Unicode formats
byte[] b=System.Text.Encoding.Unicode.GetBytes(s);
enum enumeration:

User-defined data type. enum values ​​start from 1, except custom ones. Separated by commas ",", integer values ​​can be assigned.

String conversion specific enumeration:

 object ← Enum.parse(type enumType,string value);

Such as:

color col=(color)Enum.parse(typeof(color),"white");

Note: If the string does not correspond to the enumeration, an error will occur.

   enum e
    {
    }

struct structure:

User-defined data type, structure type. Structures can contain constructors, constants, fields, methods, properties, indexers, and operators.

The structure is a value type and the address is allocated on the stack

    结构和类都可以继承接口。

    结构不能被集成，类可以。

    结构没有析构函数，类有。

 struct s
    {
    }

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