C ＃ basic knowledge (1)

Write it at the front

C# ( The English name is CSharp) ..NET It's a development platform , and C# It's a kind of .NET The programming language used on the development platform

1、 first C# Program

namespace test
{
    
    class Program
    {
    
        static void Main(string[] args)
        {
    
			//  This is the note 
            Console.Write(" first  C#  Program , ");
            Console.WriteLine(" This is the first console program ");
        }
    }
}

• The first 11 Go to the first place 13 Line is Main Method , There can only be one in each class
• Console.Write(); // Print , Console.WriteLine(); // Line to print

2、 Basic data type

Integer types

class type	Value range
sbyte	Signed number , Occupy 1 Bytes ,-27〜27-1
byte	An unsigned number , Occupy 1 Bytes ,0〜28-1
short	Signed number , Occupy 2 Bytes ,-215〜215-1
ushort	An unsigned number , Occupy 2 Bytes ,0〜216-1
int	Signed number , Occupy 4 Bytes ,-231〜231-1
uint	An unsigned number , Occupy 4 Bytes ,0〜232-1
long	Signed number , Occupy 8 Bytes ,-263〜263-1
ulong	An unsigned number , Occupy 8 Bytes ,0〜264-1

floating-point

class type	Value range
float	Single precision floating point , Occupy 4 Bytes , Keep at most 7 Decimal place
double	Double precision floating point , Occupy 8 Bytes , Keep at most 16 Decimal place

Other types

class type	explain
char	Character , for example ‘a’、‘ in ’ etc.
String	String type , for example “abc”、“123” etc. (String Not a basic data type )
bool	Boolean , Only true and false Two values

4、 Various symbols

4.1、 Escape character

Escape character	explain
\’	Single quotation marks
\"	Double quotes
\	The backslash
\0	empty
\a	Warning （ Produce a beep ）
\b	Backspace
\f	Change the page
\n	Line break
\r	enter
\t	Horizontal tabs
\v	Vertical tabs

4.2、 Arithmetic operator

Operator	say bright
+	Add
-	Subtraction
*	Multiplication
/	division
%	Remainder

example ：

class Program
{
    
    static void Main(string[] args)
    {
    
        Console.WriteLine(" Thousand bit " +1234 / 1000);
        Console.WriteLine(" Hundred bit " + 1234 / 100 % 10);
        Console.WriteLine(" ten " + 1234 / 10 % 10);
        Console.WriteLine(" bits " + 1234 % 10);
        Console.WriteLine(" Connection string ：" + "123" + "456");
    }
}

4.3、 Logical operators

Logical operators	explain
&&	Logic and , If both sides of the operator are True, Then the whole expression is True, Otherwise False; If the left operand is False, The expression on the right is not evaluated , amount to “ And ” The meaning of
||	Logic or , If one or both sides of the operator are True, The whole expression is True, Otherwise False; If left is True, The expression on the right is not evaluated , amount to “ or ” The meaning of
!	Logic is not , Represents logic contrary to the original logic

4.4、 Comparison operator

Operator	say bright
==	Equal to the judge
!=	Don't wait to judge
>	Indicates that the value of the left expression is greater than the value of the right expression
<	Indicates that the value of the left expression is less than the value of the right expression
>=	Indicates that the value of the expression on the left is greater than or equal to the value of the expression on the right
<=	Indicates that the value of the expression on the left is less than or equal to the value of the expression on the right

4.5、 An operator

Operator	explain
&	Bitwise AND . Both operands are 1, Then the whole expression is 1, Otherwise 0; You can also compare Boolean values , amount to “ And ” operation , But not short circuiting
|	Press bit or . Both operands are 0, Then the whole expression is 0, Otherwise 1; You can also compare Boolean values , amount to “ or ” operation , But not short circuiting
~	Bitwise non . When the calculated value is 1 when , The result of operation is 0; When the calculated value is 0 when , The result of operation is 1. This operator cannot be used for Boolean . Negate a positive integer , Add... To the original number 1, Then take a negative number ; Negate negative integers , Add... To the original number 1, Then take the absolute value
^	Bitwise XOR . Only two different results of the operation are 1, Otherwise 0
<<	Move left . Move the operand on the left of the operator to the left by the specified number of digits on the right of the operator , The part on the right that is vacated due to movement repair 0
>>	Move the sign right . Move the operand on the left of the operator to the right by the specified number of digits on the right of the operator . If it's a positive value , The part left vacant due to movement is filled 0; If it's negative , The part left vacant due to movement is filled 1
>>>	unsigned right shift . and >> They move in the same way , Just no matter positive or negative , All the parts vacated due to movement are filled 0

4.6、 Ternary operator

Boolean expression ? expression 1: expression 2

class Program
{
    
    static void Main(string[] args)
    {
    
        Console.WriteLine("10 by ："+(10 % 2 == 0 ? " even numbers ":" Odd number "));
    }
}

4.7、 Assignment operator

Symbol	explain
=	x=y, The value to the right of the equal sign is given to the variable to the left of the equal sign , That is, the variable y The value of is assigned to the variable x
+=	x+=y, Equate to x=x+y
-=	x-=y, Equate to x=x-y
*=	x*=y, Equate to x=x*y
/=	x/=y, Equate to x=x/y
%=	x%=y, Equate to x=x%y, Express and seek x Divide y The remainder of
++	x++ or ++x, Equate to x=x+1
–	x-- or --x, Equate to x=x-1

4.8、 Operator precedence

Operator	associativity
.（ spot ）、()（ parentheses ）、[]（ brackets ）	From left to right
+ （ just ）、-（ negative ）、++ （ Self increasing ）、–（ Self reduction ）、~（ Bitwise non ）、!（ Logic is not ）	From right to left
* （ ride ）、/ （ except ）、% （ Remainder ）	From left to right
+ （ Add ）、-（ reduce ）	From left to right
<<、>>、>>>	From left to right
<、<=、>、>=	From left to right
==、!=	From left to right
&	From left to right
|	From left to right
^	From left to right
&&	From left to right
||	From left to right
?:	From right to left
=、+=、-=、*=、/=、%=、&=、	=、^=、~=、<<=、>>=、>>>=

5、 Variables and constants

Examples of variable use

class Program
{
    
    static void Main(string[] args)
    {
    
        int num1 = 100;
        double num2 = 100.123;
        bool isFlag = true;
        String name = "Hello";

		//  Variable conversion 
        int temp;
        temp = a;
        a = b;
        b = temp;
    }
}

const The variables defined are constants , The value cannot be changed after the first assignment

    static void Main(string[] args)
    {
    
        const double PI = 3.14;
    }

6、 Naming rules

Variable name ： Hump named , The first letter of the first word is lowercase .
Name of constant ： All capitals .
The name of the class ： title case , Such as Student.
Name of interface ： It's usually based on I start , The second letter is also capitalized , Such as ICompare.
Method name ： title case , Usually use verbs , Such as AddUser.