Go language, array, pointer, structure

1. Array

Statement

Go Language array declaration needs to specify the element type and number of elements , The syntax is as follows ：

var variable_name [SIZE] variable_type

The above is the definition of one-dimensional array . For example, the following defines an array balance The length is 10 The type is float32：

var balance [10] float32

Initialize array

balance := [5]float32{
    1000.0, 2.0, 3.4, 7.0, 50.0}

If the length of the array is uncertain , have access to ... Instead of the length of the array , The compiler will infer the length of the array according to the number of elements ：

balance := [...]float32{
    1000.0, 2.0, 3.4, 7.0, 50.0}

If you set the length of the array , We can also initialize elements by specifying subscripts ：

//  Index is  1  and  3  Element initialization of 
balance := [5]float32{
    1:2.0,3:7.0}

Accessing array elements

package main

import "fmt"

func main() {
    
	var n [10]int
	var i, j int
	for i = 0; i < 10; i++ {
    
		n[i] = i + 521
	}
	for j = 0; j < 10; j++ {
    
		fmt.Printf("%d\n", n[j])
	}
}
-------------------------
 Output ：
521
522
523
524
525
526
527
528
529
530

---

2. The pointer

Address of variable in memory

package main

import "fmt"

func main() {
    
	var a int = 521
	fmt.Println(&a)
}
----------------------
 Output ：0xc000018098

What is a pointer

A pointer variable points to the memory address of a value .

Similar to variables and constants , You need to declare pointers before using them . The format of the pointer declaration is as follows ：

var var_name *var-type

var-type Is pointer type ,var_name Is the pointer variable name ,* The sign is used to specify that the variable is used as a pointer . Here is a valid pointer declaration ：

var ip *int        /*  Directed integer */
var fp *float32    /*  Point to floating point  */

Use the pointer

package main

import "fmt"

func main() {
    
	var a int = 521
	var ip *int
	ip = &a
	fmt.Println(a, ip, *ip)
}
------------------------------
 Output ：
521 0xc000018098 521

Null pointer

When a pointer is defined and not assigned to any variable , Its value is nil.

nil A pointer is also called a null pointer .

nil Conceptually and in other languages null、None、nil、NULL equally , Both refer to zero value or null value .

A pointer variable is usually abbreviated to ptr.

Null pointer judgment ：

if(ptr != nil)     /* ptr  It's not a null pointer  */
if(ptr == nil)    /* ptr  Is a null pointer  */

---

3. Structure

Structure definition needs to use type and struct sentence .struct Statement to define a new data type , A structure has one or more members .type Statement sets the name of the structure . The format of the structure is as follows ：

package main

import "fmt"

type Books struct {
    
	title   string
	author  string
	subject string
	id      int
}

func main() {
    
	var Book1 Books /*  Statement  Book1  by  Books  type  */
	Book1.title = "Go Language express "
	Book1.author = "dahe"
	Book1.subject = "Go"
	Book1.id = 1
	fmt.Println(Book1.title, Book1.author, Book1.subject, Book1.id)
}
------------------------
 Output ：
Go Language express  dahe Go 1

Copyright notice ： This tutorial is based on the rookie tutorial