for-loop - 如果有 scanf，为什么循环时会得到重复的输出？

Question

当用户输入错误的数字时，代码期望显示一次输出消息，但这是重复的。为什么？

注意:似乎是循环内的 scanf 的问题，因为如果我单独使用 scan，它会按预期工作。

无论如何，我不明白为什么会有这种行为

package main

import (
  "fmt"
  "math/rand"
  "time"
)

func main(){
  rand.Seed(time.Now().UnixNano())

  var number int = rand.Intn(99)  
  var input int = 0

  fmt.Println("random: ", number)

  fmt.Println("enter a number: ")
  fmt.Scanf("%d",&input)

  for {
    if number != input {
      fmt.Println("wrong! try again:")
      fmt.Scanf("%d",&input)
      continue
    } else {
      fmt.Println("that's correct!")
      break
    }
  }
}

Answer 1

要适应 Windows，请编写 fmt.Scanf("%d\n", &input):

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    rand.Seed(time.Now().UnixNano())

    var number int = rand.Intn(99)
    var input int = 0

    fmt.Println("random: ", number)

    fmt.Println("enter a number: ")
    fmt.Scanf("%d\n", &input)

    for {
        if number != input {
            fmt.Println("wrong! try again:")
            fmt.Scanf("%d\n", &input)
            continue
        } else {
            fmt.Println("that's correct!")
            break
        }
    }
}

输出:

random:  84
enter a number: 
42
wrong! try again:
42
wrong! try again:
84
that's correct!

<小时/>

Windows 使用 "\r\n" 作为行尾。 Linux 和其他操作系统使用 "\n" 表示行尾。

您没有检查 Scanf 错误。

package main

import (
    "fmt"
    "math/rand"
    "time"
)

func main() {
    rand.Seed(time.Now().UnixNano())

    var number int = rand.Intn(99)
    var input int = 0

    fmt.Println("random: ", number)

    fmt.Println("enter a number: ")
    n, err := fmt.Scanf("%d", &input)
    if err != nil {
        fmt.Println(n, err)
    }

    for {
        if number != input {
            fmt.Println("wrong! try again:")
            n, err := fmt.Scanf("%d", &input)
            if err != nil {
                fmt.Println(n, err)
            }
            continue
        } else {
            fmt.Println("that's correct!")
            break
        }
    }
}

输出(Windows):

random:  84
enter a number:
42
wrong! try again:
0 unexpected newline
wrong! try again:
42
wrong! try again:
0 unexpected newline
wrong! try again:
84
that's correct!

Windows 将 “42\r\n” 扫描为 “42\r” 和 “\n”。

输出(Linux):

random:  84
enter a number: 
42
wrong! try again:
42
wrong! try again:
84
that's correct!

Linux 扫描“42\n”。