条件语句

1.if

package main
import "io/ioutil"
func main() {
    const filename = "abc.txt"
    // 写法1
    contents, err := ioutil.ReadFile(filename)
    if err != nil{
        fmt.Println(err)
    } else {
        fmt.Printf("%s\n", contents)
    }
    // 写法2
    // if的条件里可以赋值
    // if的条件里赋值的变量作用域就在这个if语句里
    if contents, err := ioutil.ReadFile(filename); err != nil {
        fmt.Println(err)
    } else {
        fmt.Printf("%s\n", contents)
    }
}

2.switch
switch会自动break，除非使用fallthrough

// 例1 switch后可以没有表达式
func grade(score int) string {
    g := ""
    switch{
    case score < 0 || score > 100:
        panic(fmt.Sprinft("Wrong score: %d", score))
    case score < 60:
        g = "F"
    case score < 80:
        g = "C"
    case score < 90:
        g = "B"
    case score <= 100:
        g = "A"
    }
    return g
}

// 例2
func eval(a, b int, op string) int {
    var result int
    switch op{
    case "+":
        result = a + b
    case "-":
        result = a - b
    case "*":
        result = a * b
    case "/":
        result = a / b
    default:
        panic("unsupported operator:" + op)
    }
    return result
}