入门学习Go的基本语法

    break        default      func         interface    select
    case         defer        go           map          struct
    chan         else         goto         package      switch
    const        fallthrough  if           range        type
    continue     for          import       return       var

    Constants:    true  false  iota  nil
        Types:    int  int8  int16  int32  int64  
                  uint  uint8  uint16  uint32  uint64  uintptr
                  float32  float64  complex128  complex64
                  bool  byte  rune  string  error
    Functions:   make  len  cap  new  append  copy  close  delete
                 complex  real  imag
                 panic  recover

var 变量名 变量类型

var name string
var age int
var flag bool

var 变量名 类型 = 表达式

var name string = "csp"
var age int = 22

var name = "csp" //自动识别为string
var age = 18 //自动识别为int

package main
import "fmt"
// 全局变量m
var m = 100
func main() {
	n := 10
	m := 200 // 此处声明局部变量m
	fmt.Println(m, n)
}

func foo() (int, string) {
	return 10, "csp"
}
func main() {
	x, _ := foo() //只接收foo 函数的第一个返回值
	_, y := foo() //只接收foo 函数的第二个返回值
	fmt.Println("x=", x)
	fmt.Println("y=", y)
}

const pi = 3.1415
const e = 2.7182

const (
    pi = 3.1415
    e = 2.7182
)

const (
    n1 = 100
    n2
    n3
)

const (
		n1 = iota //0
		n2        //1
		n3        //2
		n4        //3
	)

const (
		n1 = iota //0
		n2        //1
		_
		n4        //3
	)

const (
		n1 = iota //0
		n2 = 100  //100
		n3 = iota //2
		n4        //3
	)
	const n5 = iota //0

const (
		_  = iota
		KB = 1 << (10 * iota)// 1 左移动 10 位 == 2^10 == 1024B = 1KB
		MB = 1 << (10 * iota)// 在原来基础上再左移动10位，2^20 == 1MB
		GB = 1 << (10 * iota)
		TB = 1 << (10 * iota)
		PB = 1 << (10 * iota)
	)

const (
		a, b = iota + 1, iota + 2 //1,2
		c, d                      //2,3
		e, f                      //3,4
	)

package main
import "fmt"
func main(){
	// 十进制
	var a int = 10
	fmt.Printf("%d \n", a)  // 10
	fmt.Printf("%b \n", a)  // 1010  占位符%b表示二进制
	// 八进制  以0开头
	var b int = 077
	fmt.Printf("%o \n", b)  // 77
	// 十六进制  以0x开头
	var c int = 0xff
	fmt.Printf("%x \n", c)  // ff
	fmt.Printf("%X \n", c)  // FF
}

package main
import (
        "fmt"
        "math"
)
func main() {
        fmt.Printf("%f\n", math.Pi)
        fmt.Printf("%.2f\n", math.Pi)
}

var c1 complex64
c1 = 1 + 2i
var c2 complex128
c2 = 2 + 3i
fmt.Println(c1)
fmt.Println(c2)

s1 := "hello"
s2 := "你好"

package main
import (
    "fmt"
)
func main() {
    fmt.Println("str := \"c:\\Code\\hello_golang\\go.exe\"")
}

s1 := `第一行
第二行
第三行
`
fmt.Println(s1)

var a := '中'
var b := 'x'

// 遍历字符串
func traversalString() {
	s := "hello沙河"
	for i := 0; i < len(s); i++ { //byte
		fmt.Printf("%v(%c) ", s[i], s[i])
	}
	fmt.Println()
	for _, r := range s { //rune
		fmt.Printf("%v(%c) ", r, r)
	}
	fmt.Println()
}

func changeString() {
	s1 := "big"
	// 强制类型转换
	byteS1 := []byte(s1)
	byteS1[0] = 'p'
	fmt.Println(string(byteS1))
	s2 := "白萝卜"
	runeS2 := []rune(s2)
	runeS2[0] = '红'
	fmt.Println(string(runeS2))
}

T(表达式)

func sqrtDemo() {
	var a, b = 3, 4
	var c int
	// math.Sqrt()接收的参数是float64类型，需要强制转换
	c = int(math.Sqrt(float64(a*a + b*b)))
	fmt.Println(c)
}

if 表达式1 {
    分支1
} else if 表达式2 {
    分支2
} else{
    分支3
}

func ifDemo1() {
	score := 65
	if score >= 90 {
		fmt.Println("A")
	} else if score > 75 {
		fmt.Println("B")
	} else {
		fmt.Println("C")
	}
}

func ifDemo2() {
	if score := 65; score >= 90 {
		fmt.Println("A")
	} else if score > 75 {
		fmt.Println("B")
	} else {
		fmt.Println("C")
	}
}

for 初始语句;条件表达式;结束语句{
    循环体语句
}

func forDemo() {
	for i := 0; i < 10; i++ {
		fmt.Println(i)
	}
}

func forDemo2() {
	i := 0
	for ; i < 10; i++ {
		fmt.Println(i)
	}
}

func forDemo2() {
	i := 0
	for ; i < 10; i++ {
		fmt.Println(i)
	}
}

for {
    循环体语句
}

s := "hello 海贼王"
for i,v := range d {
    fmt.Printf("%d %c\n",i,v);
}
// 输出结果
0 h
1 e
2 l
3 l
4 o
5
7 海
8 贼
9 王

func switchDemo1() {
	finger := 3
	switch finger {
	case 1:
		fmt.Println("大拇指")
	case 2:
		fmt.Println("食指")
	case 3:
		fmt.Println("中指")
	case 4:
		fmt.Println("无名指")
	case 5:
		fmt.Println("小拇指")
	default:
		fmt.Println("无效的输入！")
	}
}

func testSwitch3() {
	switch n := 7; n {
	case 1, 3, 5, 7, 9:
		fmt.Println("奇数")
	case 2, 4, 6, 8:
		fmt.Println("偶数")
	default:
		fmt.Println(n)
	}
}

func switchDemo4() {
	age := 30
	switch {
	case age < 25:
		fmt.Println("好好学习吧")
	case age > 25 && age < 35:
		fmt.Println("好好工作吧")
	case age > 60:
		fmt.Println("好好享受吧")
	default:
		fmt.Println("活着真好")
	}
}

func switchDemo5() {
	s := "a"
	switch {
	case s == "a":
		fmt.Println("a")
		fallthrough
	case s == "b":
		fmt.Println("b")
	case s == "c":
		fmt.Println("c")
	default:
		fmt.Println("...")
	}
}

func gotoDemo1() {
	var breakFlag bool
	for i := 0; i < 10; i++ {
		for j := 0; j < 10; j++ {
			if j == 2 {
				// 设置退出标签
				breakFlag = true
				break
			}
			fmt.Printf("%v-%v\n", i, j)
		}
		// 外层for循环判断
		if breakFlag {
			break
		}
	}
}

func gotoDemo2() {
	for i := 0; i < 10; i++ {
		for j := 0; j < 10; j++ {
			if j == 2 {
				// 设置退出标签
				goto breakTag
			}
			fmt.Printf("%v-%v\n", i, j)
		}
	}
	return
	// 标签
breakTag:
	fmt.Println("结束for循环")
}

func breakDemo1() {
BREAKDEMO1:
	for i := 0; i < 10; i++ {
		for j := 0; j < 10; j++ {
			if j == 2 {
				break BREAKDEMO1
			}
			fmt.Printf("%v-%v\n", i, j)
		}
	}
	fmt.Println("...")
}

func continueDemo() {
forloop1:
	for i := 0; i < 5; i++ {
		// forloop2:
		for j := 0; j < 5; j++ {
			if i == 2 && j == 2 {
				continue forloop1
			}
			fmt.Printf("%v-%v\n", i, j)
		}
	}
}