Golang 教程1

注意，该文档只适合有编程基础的同学，这里的go教程只给出有区别的知识点

[go教程](‘Go基础 · Go语言中文文档 (topgoer.com)’)

一、基础

tip: 下划线_ 可以起到忽略的作用

运行以下命令来初始化一个新的 Go 模块：

// 如你的项目在 gocode/testproject01/unit2/demo01 中 （从src后开始， 用‘/’隔开）。
go mod init gocode/testproject01/unit2/demo01 
//1、go mod init：这是 Go 的模块初始化命令，用于创建一个新的 go.mod 文件，它是 Go 模块的元数据文件，用于记录模块的基本信息和依赖关系。
//2、gocode/testproject01/unit2/demo01：这是你指定的模块名称。这个名称将成为你的模块在 Go 生态系统中的唯一标识符。


//输入操作
_, err := fmt.Scanf("%v", &name) //录入数据的时候，类型一定要匹配。

// _：这是一个空白标识符，在 Go 语言中用来忽略赋给它的值。 
//1、 fmt.Scanln 函数返回两个值：第一个是扫描的元素数量，第二个是错误（如果有）。因为我们只关心错误（第二个返回值），所以我们使用 _ 来忽略第一个返回值。
//2、 err：这是用来存储 fmt.Scanln 函数返回的错误值。如果函数执行成功，则 err 将为 nil；如果发生错误，则 err 将包含具体的错误信息。
//3、 :=：这是一个短声明语法，用于声明并初始化一个变量。在这里，我们声明了一个名为 err 的变量，并将其初始化为 fmt.Scanln(&a) 函数的第二个返回值。
//4、 fmt.Scanln(&a)：这是 fmt.Scanln 函数调用，它从标准输入读取数据，并尝试将读取的数据转换成变量 a 的类型（这里是整型 int）。它需要一个变量的引用作为参数，这里使用了 &a。

1、 自动缩进

gofmt -w xxx.go 

2、 关于赋值, 支持这种声明

sex := "man"
var n4, name, n5 = 10, "jack", 7.8
n6, height := 6.9, 100.6

3、全局赋值， 省时省力

var (
	n9 = 100
	n10 = "dasda"
)

//导入包也可以如此操作, 如
import (
    "fmt"
    "strconv"
)

4、字符串一旦定义好，值不可变

name = "黎明"
name[0] = "牛" //会报错

5、 如果字符串需要赋值特殊的字符（关键字、<、= …），用反单引号包裹

str := `
	var a string = 1
	string a < 1231
`

6、类型转换 T() 显示转化, T为你想要转换的类型

a := 100
b := float32(a)
fmt.Println(a, b)
//注意，类型大的转化至类型小的变量，高位部分会被截断

var n1 int64 =  888888888
var n2 = int8(n1)
fmt.Println(n2)
fmt.Printf("%T", n2c)

``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01> go run .\main.go
56
int8
``````````````````````````````````````````````````````````````````````````````````````````````````

var n3 int32 = 12 
//会报错， var n4 int64 = int64(n3) + 30
var n4 int8 = n3 + 30 
fmt.Println(n3)
fmt.Println(n4)

``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01> go run .\main.go
# command-line-arguments
.\main.go:5:16: cannot use n3 + 30 (value of type int32) as int8 value in variable declaration
``````````````````````````````````````````````````````````````````````````````````````````````````

7、 string类型转化，strconv.parseInt等函数返回的是2个值（value， err）所以应有2个变量承接

func main() {
	str := "123"
	i, err := strconv.Atoi(str)
	if err != nil {
		fmt.Println(err)
	} else {
		fmt.Println(i)
	} 
}

``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01>  go run .\main.go
123
``````````````````````````````````````````````````````````````````````````````````````````````````

8、 指针

func main() {
	var a int = 10
	var ptr *int = &a
	fmt.Println("Value of a is ", a)
	fmt.Println("Value of a is ", *ptr)
	fmt.Println("Address of a is ", ptr)
	fmt.Println("Address of a is ", &a)
	fmt.Println("Address of a is ", &ptr)
	*ptr = 20
	fmt.Println("Value of a is ", a)
} 

``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01>  go run .\main.go  
Value of a is  10
Value of a is  10
Address of a is  0xc00000a0f8
Address of a is  0xc00000a0f8
Address of a is  0xc000078050
Value of a is  20
`````````````````````````````````````````````````````````````````````````````````````````````````

9、分支控制

//单、多分支， 注意：条件表达式可以不写，也建议不写
if 条件表达式 {
   逻辑代码
} else if 条件表达式 {
   逻辑代码
} else {
   逻辑代码 
}

// switch 不用额外加break 防止代码穿透
switch 条件表达式 {
    case 条件满足1：
    	xxx
    case 条件满足2：
    	xxx
    。。。
    default:
    	XXX
}

// 如：
func main() {
	var a int 
	fmt.Println("请输入数字：")
	_, err := fmt.Scanln(&a)
	if err != nil {
		fmt.Println("输入错误:", err)
		return
	}
	if a == 1 {
		fmt.Println("a = 1")
	} else if a == 2 {
		fmt.Println("a = 2")
	} else {
		fmt.Println("a = 3")
	}

} 

//可以使用 fallthrough 穿透，但只能穿透一层

10、 循环 （go里面没有while循环）

//跟c语言一样，条件表达式不用（）包裹
func main() {
	i, sum := 0, 0 
	for i = 0; i < 10; i++ {
		sum += i
	}
	fmt.Println(sum)
} 
``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01> go  run .\main.go
45
``````````````````````````````````````````````````````````````````````````````````````````````````
//可以跟while一样, 格式灵活
func main() {
	for {
		fmt.Println("hello Golang")
	}
} 
``````````````````````````````````````````````````````````````````````````````````````````````````
(base) PS E:\Goproject\src\gocode\testproject01\unit2\demo01> go  run .\main.go
hello Golang
hello Golang
hello Golang
hello Golang
hello Golang
。。。
``````````````````````````````````````````````````````````````````````````````````````````````````

10.1 for range （Go 特有，可以遍历数组、切片、字符串、map以及通道，形式上有点类似于foreach）

func main() {
	str := "hello world"
	for i := 0; i < len(str); i++ {
		fmt.Printf("%c", str[i])
	}
} 

//等效于
// 这里的 fmt.Printf("索引为 %d, 对应的值为 %c \n", i, val) 是带格式的输出， 可以类比 fmt.Println()
func main() {
	str := "hello world"
	for i, val  := range str {
		fmt.Printf("索引为 %d, 对应的值为 %c \n", i, val)
	}
}