if switch

  1. if

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    const filename = "a.txt"
    contents,err :=ioutil.ReadFile(filename)
    if err != nil {
    	fmt.Println(err)
    }else {
    	fmt.Printf("%s",contents)
    }

    //简写版本
    const filename = "a.txt"
    if 	contents,err :=ioutil.ReadFile(filename) ; err != nil {
    	fmt.Println(err)
    }else {
    	fmt.Printf("%s",contents)
    }
    //只在if 作用域内

    ​

  2. switch

    switch 默认带上braek 除非显式指定fallthrough

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    var res int
    switch op {
    case "+":
    	res = a+b
    case "-":
    	res = a-b
    case "*":
    	res = a*b
    case "/":
    	res = a/b
    	fallthrough
    case "p":
    	fmt.Println("hello")
    default:
    	panic("undefine opcode:" + op)
    }
    fmt.Println(res)
    //hello
    //0
    //不携带参数
    var res int
    flag := rand.Int()
    switch {
    case op == "+":
    	res = a + b 
    case flag > 10000:
        res = 1
    //...
    }
    fmt.Println(res)

    ​