为什么在有scanf的循环中，为什​​么会得到重复的输出？

Question

When the user enters a wrong number, the code expects to show once the output message but this it's duplicated. why?

note: seems to be something with the scanf inside the loop because if I use scan lonely it works as expected.

Anyway, I can't understand why this behavior

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

To accomodate Windows, write fmt.Scanf("%d ", &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
", &input)

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

Output:

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

---

Windows uses " " for end-of-line. Linux and others use " " for end-of-line.

You did not check for Scanf errors.

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
        }
    }
}

Output (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 Scans "42 " as "42" and " ".

Output (Linux):

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

Linux Scans "42 ".