2. Basic knowledge of golang

Catalog

1. identifier

2. keyword

3. Naming specification ( Suggest )

4. Variable

5. Constant

6. Data type classification

7. Basic supplement  

8. Boolean type

9. Numeric type

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1. identifier

 identifier ： Just name it , The composition rules are as follows 
  1. Identifiers are made up of letters , Numbers and underscores 
  2. Cannot start with a number 
  3. Identifiers are case sensitive 

2. keyword

1. Keywords are built-in characters , Cannot be used as an identifier 
2. common 25 Two keywords and 36 Predefined identifiers 
3. Don't have to remember , You'll get familiar with it slowly 

3. Naming specification ( Suggest )

1.Go It's case sensitive language 
2. When an identifier is referenced as an external package , The first letter should be capitalized 
   When the identifier is not visible by outsourcing , Initial lowercase 
3. Package name ：
     Any one of them go Files can be referenced as packages ,
     After naming the package name (package  Package name ) when , Try to keep consistent with the directory , Or meaningful 
4.go File naming ： A lowercase letter  +  Underline 
5. Structure naming ： Hump nomenclature 
6. The interface name ： With "er" ending 
7. Constant naming ： All capitals  +  Underline 
8. unit testing ： The file is named with "_test.go" ending , The function name is "Test" start 

4. Variable

1. The variable of reputation cannot be repeated , And after the declaration, you must use 
2. Externally declared variables ：var  Variable name   Variable type 
3. Batch variable declaration ：
    var(
        name string
	    sex  string
	    age  int
    )

4. Variable initialization ： use  =  assignment 
    var name = "fly"

5. Variable type derivation ： During initialization , Don't declare data types ,go Internal will automatically deduce 
    var(
        name = "fly"
        age = 18
        sex = "man"
    )

6. Initialize multiple variables ： Separated by commas , One to one assignment 
    var name, age, sex = "fly", 18, "man"

7. Short variable declaration ： Refers to variables declared inside a function , You don't have to write var, use ":="
    fun main() {
        name := "zcy"
        age = 18
        sex = "man"
    }


8. Anonymous variables ： When receiving variables as parameters , Unused variables are underlined "_" Instead of 
    package main
    import "fmt"

    func getNameAge() (string, int) {
        return "fly", 18
    }
    func main()  {
        name, _ := getNameAge()
        fmt.Printf("name: %v\n", name)
    }

9. notes ：
     Single-line comments ： Double diagonal bar //     ctrl + /
     Multiline comment ：/*  */      alt + shif t+ a

5. Constant

1. Concept ： Constants are defined in the compilation stage , Unalterable 
2. Constant definition ： Use keywords  const
       usage ：const  Constant names   type  =  Constant values 

3. Because when defining constants, you must assign values , So constant types can be omitted 

4. Batch definition constants 
    const (
        width = 100
        height = 100
    )

5. When defining constants in batch , If the following constant omits the assignment , The default is the same as the previous variable 
    const (
        hight = 100     // 100
        weidth          // 100
        name = "fly"    // fly
        age             // fly
    )

6. Continuous definition ( Multiple assignments )：
    const width, height = 100, 100

7.iota
    (1)iota Is a constant that can be modified by the compiler , The default is 0, Every time you call +1, encounter const When the reset to 0
    (2) Both constants define iota, There is a gap between the two "_" Or ordinary constants ,iota The value of will still jump 
        const (
            a = iota	// 0
            _           //       encounter "_",iota still +1, here =1
            b = iota    // 2
            c = 1		// 1     Encountered a common variable ,iota still +1, here =3
            d = iota	// 4
        )

6. Data type classification

1. Boolean type 
2. Numeric type （ integer , floating-point ）
3. String type （ Fixed length ）
4. Derived type （ Pointer types , An array type , Structured type ,Channel type , Function type , Slice type , Interface type (interface),Map type ）

7. Basic supplement  

1. Judge if
    if  Conditions  {
         The body of the function 
    } else {
         The body of the function 
    }

2. loop for
    for  The initial state ;  Conditions ;  State change  {
         The body of the function 
    }

3. And ：&&

4. Print variables 
    fmt.Println( Variable )
5. Format printing 
    fmt.Printf("%v\n",  Variable )

 difference ：Println Bring your own line feed 

5. Print symbols 
     Print data ：%v
        fmt.Printf("%v\n", "FLY")    // FLY
     Print data type ：%T
        fmt.Printf("%T\n", "fly")    // string
     Print number type integer size ：%dB
        fmt.Printf("%dB\n", 18)      // 18B

8. Boolean type

true,false
 effect : In conditional judgment , loop , Logical expression, etc , Used to judge true or false 
 Be careful :golang Boolean type in , You can't use numbers (0 Or not 0) Express true and false 
package main

import "fmt"
func main() {
	age = 200

    //  error 
	if age {
		fmt.Println(" error ")
	}

    //  correct 
	if age>1 {
		fmt.Println(" correct ")
	}
}

9. Numeric type

    1. Include ： Integer and floating point , Primitive plural , Bit operation uses complement 
        
    2. integer ：int integer ,uint Unsigned integer ,uintptr Unsigned integer with fixed length to store pointer 

    3.int And uint stay 32 Bit on the operating system 4 Bytes , stay 64 Bit on the operating system 8 Bytes 

    4.go The sizes of the types in are fixed ( understand ), among int Type is the fastest kind of calculation 
        
    5. floating-point ：float32 And float64( Add ： Floating point numbers in computers are imprecise ！)
        （1） The integer zero value is 0, Floating point zero is 0.0
        （2） Format and print floating point ：
                 Full print ：%f
                 Take two digits to print ：%.2f
    
    6. Hexadecimal conversion   Binary format output 
         Decimal system ：%d
         Binary system ：%b
         octal ：%o
         Hexadecimal ：%x  or %X
    
    7. The plural ：
        32 position ：complex64
        64 position ：complex128