《Go语言编程》calc.go的错误

最近看由人民邮电出版社许式伟 吕桂华等编著《Go语言编程》【第1章初识Go语言】【1.5 工程管理】时，发现了示例代码calc.go有几处错误，args := os.Args数组变量args[0]代表程序自身，3个if语句len(args)条件判断右值也都小了1，按照书本编写代码运行时将会一直执行匿名函数Usage(),显示如下：

USAGE: calc command [arguments] ...

The commands are:
        add     Addition of two values.
        sqrt    Square root of a non-negative value.

正确的calc.go代码如下：

// calc.go
   package main
   
   import (
       "fmt"
       "os"
       "simplemath"
       "strconv"
   )
   
   var Usage = func() {
       fmt.Println("USAGE: calc command [arguments] ...")
       fmt.Println("\nThe commands are:\n\tadd\tAddition of two values.\n\tsqrt\tSquare root of a non-negative value.")
   }
   
   func main() {
       args := os.Args
       if args == nil || len(args) < 3 {
           Usage()
           return
       }
   
       switch args[1] {
       case "add":
           if len(args) != 4 {
               fmt.Println("USAGE: calc add <integer1><integer2>")
               return
           }
           v1, err1 := strconv.Atoi(args[2])
           v2, err2 := strconv.Atoi(args[3])
           if err1 != nil || err2 != nil {
               fmt.Println("USAGE: calc add <integer1><integer2>")
               return
           }
           ret := simplemath.Add(v1, v2)
           fmt.Println("Result: ", ret)
       case "sqrt":
           if len(args) != 3 {
               fmt.Println("USAGE: cale sqrt <integer>")
               return
           }
           v, err := strconv.Atoi(args[2])
           if err != nil {
               fmt.Println("USAGE: calc sqrt <integer>")
               return
           }
           ret := simplemath.Sqrt(v)
           fmt.Println("Result: ", ret)
       default:
           Usage()
       }
   }

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