Go条件语句

package main

import (
    "io/ioutil"
    "fmt"
)

// switch语句
// switch会自动break 除非使用fallthrough
// switch后可以没有表达式
func eval(a, b int, op string) int {
    var reslut int
    switch op {
    case "+":
        reslut = a + b
    case "-":
        reslut = a - b
    case "*":
        reslut = a * b
    case "/":
        reslut = a / b
    default:
        panic("unsupported operator:"+op)
    }
    return reslut
}

func grade(soure int) string {
    g := ""
    switch {
    case soure < 60:
        g = "F"
    case soure < 80:
        g = "C"
    case soure < 90:
        g = "B"
    case soure < 100:
         g = "A"
    case soure < 0 || soure > 100:
        panic(fmt.Sprintf("wrong soure : %d", soure))
    }
    return g
}


func main() {

    // if语句
    // if的条件里不需要括号
    // 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
    const filename =  "abc.txt"

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

    if contents, err := ioutil.ReadFile(filename); err != nil {
        fmt.Println(err)
    } else  {
        fmt.Printf("%s\n",contents)
    }


    fmt.Println(grade(50), grade(70), grade(85), grade(95))
    //fmt.Println(grade(-5), grade(105))
}