英文:
Why the input of Scanf is always 0?
问题
我正在尝试从用户那里获取输入并将其打印出来，但是在我输入一些内容后，距离的值似乎是0。
以下是代码：
type Person struct {
name string
age int
ambition string
}
func (p *Person) walking() {
var distance int
fmt.Println("输入距离")
fmt.Scanf("%f", &distance)
if distance < 9 {
fmt.Println(p.name, "正在向那个方向行走，距离为", distance,
"千米")
} else {
fmt.Println("这是一个错误，请忽略")
}
}
func main() {
p := new(Person)
p.name = "Joker"
p.walking()
}
正如你所看到的，无论我在主函数中运行这个命令多少次，它总是打印出fmt.Println(p.name, "正在向那个方向行走，距离为", distance, "千米")，即使距离的值大于9。
p.walking() 总是打印出距离为0？有人能解释一下这里发生了什么吗？
英文:
I'm trying to get input from a user and print it out, but apparently the value of the distance is 0, after I did some input.
Here's the code:
type Person struct {
name string
age int
ambition string
}
func (p *Person) walking() {
var distance int
fmt.Println("Enter the distance")
fmt.Scanf("%f", &distance)
if distance < 9 {
fmt.Println(p.name, " is walking towards that direction in ", distance,
"kilometer")
} else {
fmt.Println("This is an error, ignore this")
}
}
As you can see whenever I try to run this command on my main function, it always prints fmt.Println(p.name, " is walking towards that direction in ", distance, "kilometer") even though the value of distance is more than 9.
func main() {
p := new(Person)
p.name = "Joker"
p.walking()
}
p.walking() will always print distance as 0? Can anyone explain to me what is going on here?
答案1
得分: 5
你使用了错误的格式字符串。%f 用于扫描浮点数，但是你的变量 distance 是整数类型 int，所以你应该使用 %d：
fmt.Scanf("%d", &distance)
或者将 distance 变量声明为浮点数类型，然后你可以使用 %f：
var distance float64
fmt.Println("Enter the distance")
fmt.Scanf("%f", &distance)
注意：
fmt.Scanf() 返回成功扫描的项目数和一个可选的错误。你应该习惯处理 Go 中的错误，这将节省你很多时间。
最简单的方法是存储和打印 Scanf() 的返回值：
var distance int
fmt.Println("Enter the distance")
n, err := fmt.Scanf("%f", &distance)
fmt.Println(n, err)
输出结果为：
0 bad verb %f for integer
这立即告诉你没有扫描到任何项目，并且出现了错误：bad verb %f for integer，这基本上是自解释的。
这也解释了为什么你总是看到打印出 0 公里：你的 distance 变量被初始化为 0（int 的零值），并且从未更改过。
如果扫描成功，你将看到以下输出：
1 <nil>
表示成功扫描了一个项目（即 distance），并且没有错误。
如果你使用一次 Scanf() 扫描多个项目，n 当然可以大于 1（例如 fmt.Scanf("%f %d", &distance, &temp)）。
英文:
You used a wrong format string. %f is used to scan floating point numbers, but your variable distance is of type int, so you should use %d:
fmt.Scanf("%d", &distance)
Or declare distance variable to be a floating point number and then you can use %f:
var distance float64
fmt.Println("Enter the distance")
fmt.Scanf("%f", &distance)
Note:
fmt.Scanf() returns the number of items successfully scanned, and an optional error. You should get used to handle errors in Go which would save you a lot of time.
As a minimal by storing and printing the return values of Scanf():
var distance int
fmt.Println("Enter the distance")
n, err := fmt.Scanf("%f", &distance)
fmt.Println(n, err)
Prints:
0 bad verb %f for integer
Which immediately tells you 0 items were scanned and there was an error: bad verb %f for integer which is pretty much self explanatory.
This also explains why you always see 0 kilomenters printed: your distance variable is initialized to 0 (zero value of int) and it is never changed.
If scanning would be successful, you would see an output of:
1 <nil>
Meaning that one item was scanned successfully (the distance) and there was no error.
If you would scan multiple items with one Scanf() call, n could be greater than 1 of course (for example fmt.Scanf("%f %d", &distance, &temp)).
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