Golang - 流程控制

1. 选择结构

if else语句:

//package 声明开头表示代码所属包
package main

import (
	"io/ioutil"
	"fmt"
)

func main() {
	//常量
	const filename = "abc.txt"

	//读取文件
	contens, err := ioutil.ReadFile(filename)

	// nil空
	if err != nil {
		fmt.Println(err)
	} else {
		fmt.Printf("%s
", contens)
	}

	// ;后边直接去判断和处理了
	if contens, err := ioutil.ReadFile(filename); err != nil {
		fmt.Println(err)
	} else {
		fmt.Printf("%s
", contens)
	}
}

switch语句:

//package 声明开头表示代码所属包
package main

import "fmt"

//函数传入成绩，得到级别 ABC
func grade(score int) string {
	//定义个空串
	g := ""

	//switch语句
	switch {
	case score < 0 || score > 100:
		g = "输入错误"
		//隐式加了一个break，匹配到了就结束
		//关键字fallthrough是继续往下跑
		fallthrough

	case score < 60:
		g = "F"
	case score < 80:
		g = "C"
	case score < 90:
		g = "B"
	case score <= 100:
		g = "A"
	}

	return g
}

func main() {
	fmt.Println(
		grade(0),
		grade(59),
		grade(60),
		grade(82),
		grade(99),
		grade(100),
		grade(-3),
	)
}

//F F C B A A F

2. 循环结构

for 语句:

//package 声明开头表示代码所属包
package main

import (
	"fmt"
	"time"
)


//1.无限死循环
func for1() {
	for {
		fmt.Println("爱天台，爱日耳曼战车")
		//睡1秒
		time.Sleep(1 * time.Second)
	}
}


//2.有限次循环
func for2() {
	for i := 1; i < 11; i++ {
		fmt.Println("爱天台，爱战车", i)
		//睡眠
		time.Sleep(500 * time.Millisecond)
	}
}


//3.if else
func for3() {
	for i := 1; i < 11; i++ {
		if i%5 == 0 {
			fmt.Println("爱阿根廷")
		} else if i%2 == 1 {
			fmt.Println("更爱战车")
		} else {
			fmt.Println("最爱是天台")
		}
		time.Sleep(500 * time.Millisecond)
	}
}


func main() {
	//for2()
	for3()
}

range 语句:

//package 声明开头表示代码所属包
package main

import "fmt"

func main() {
	s := "abc"

	//1.接收了下标，通过下标取值
	for i := range s {
		fmt.Printf("下标=%d,值=%c
", i, s[i])
	}

	//2.直接接收下标和元素值
	for i, c := range s {
		fmt.Printf("下标2=%d,值2=%c
", i, c)
	}

	//3.忽略下标
	for _, c := range s {
		fmt.Printf("值=%c
", c)
	}
}

//下标=0,值=a
//下标=1,值=b
//下标=2,值=c
//下标2=0,值2=a
//下标2=1,值2=b
//下标2=2,值2=c
//值=a
//值=b
//值=c

3. 跳转语句

break和continue

//package 声明开头表示代码所属包
package main

import "fmt"

func main() {
	for i :=0; i<5; i++{
		if 2==i{
			//break
			continue
		}
		fmt.Println(i)
	}
}

//0
//1
//3
//4

goto：可以跳转到指定的位置运行，注意是跳转到当前函数内

//package 声明开头表示代码所属包
package main

import "fmt"

func main() {
	for i :=0; i<5; i++{
		fmt.Println(i)

		//关键字goto
		goto LABEL
	}
	fmt.Println("程序结束")
LABEL:
	fmt.Println("程序over")
}

//0
//程序over