英文:
How do I update a value of a variable in an if statement in Go?
问题
我正在尝试学习Go语言，并创建了一个函数。在这个函数中，我声明了一个名为game_ratio的变量，并将其设置为0.0。然后我使用一个if语句来尝试更新game_ratio的值。但是当我尝试编译时，我收到以下错误信息：
'game_ratio declared and not used'
以下是我的函数代码：
func gameRatio(score1 int, score2 int, max_score float64) float64 {
var game_ratio float64 = 0.0
var scaled_score_1 = scaleScore(score1, max_score)
var scaled_score_2 = scaleScore(score2, max_score)
fmt.Printf("Scaled score for %v is %v\n", score1, scaled_score_1)
fmt.Printf("Scaled score for %v is %v\n", score2, scaled_score_2)
if score1 > score2 {
game_ratio := (scaled_score_1+1.0)/(scaled_score_1+scaled_score_2+2.0) + 1.0*0.5
}
return game_ratio
}
以下是调用该函数的代码：
func main() {
flag.Parse()
s1 := flag.Arg(0)
s2 := flag.Arg(1)
i1, err := strconv.Atoi(s1)
i2, err := strconv.Atoi(s2)
if err != nil {
fmt.Println(err)
os.Exit(2)
}
fmt.Println("Game ratio is", gameRatio(i1, i2, 6))
}
我还编写了另一个名为scaleScore的函数。如果我移除if语句，代码就可以正常工作。
要运行我的应用程序，我输入'rankings 28 24'。
英文:
I'm trying to learn Go and I've created a function where I declare a variable game_ratio and set it to 0.0. I then have an if statement where I try and update the value of game_ratio. When I try and compile, I get the following error message:
'game_ratio declared and not used'
Here's my function:
func gameRatio(score1 int, score2 int, max_score float64) float64 {
var game_ratio float64 = 0.0
var scaled_score_1 = scaleScore(score1, max_score)
var scaled_score_2 = scaleScore(score2, max_score)
fmt.Printf("Scaled score for %v is %v\n", score1, scaled_score_1)
fmt.Printf("Scaled score for %v is %v\n", score2, scaled_score_2)
if score1 > score2 {
game_ratio := (scaled_score_1+1.0)/(scaled_score_1+scaled_score_2+2.0) + 1.0*0.5
}
return game_ratio
}
Here's the code to call it:
func main() {
flag.Parse()
s1 := flag.Arg(0)
s2 := flag.Arg(1)
i1, err := strconv.Atoi(s1)
i2, err := strconv.Atoi(s2)
if err != nil {
fmt.Println(err)
os.Exit(2)
}
fmt.Println("Game ratio is", gameRatio(i1, i2, 6))
}
ScaleScore is another function I have written. If I remove the if statement, the code works.
To run my app, I type 'rankings 28 24'
答案1
得分: 4
短变量声明重新声明了game_ratio。
使用赋值语句进行修改：
game_ratio = (scaled_score_1+1.0)/(scaled_score_1+scaled_score_2+2.0) + 1.0*0.5
短变量声明是一种简写形式，它使用以下语法：
ShortVarDecl = IdentifierList ":=" ExpressionList
它相当于一个带有初始化表达式但没有类型的常规变量声明：
"var" IdentifierList = ExpressionList
与常规变量声明不同，短变量声明可以重新声明变量，前提是它们在同一代码块中以相同的类型进行了原始声明，并且至少有一个非空白变量是新的。因此，重新声明只能出现在多变量的短声明中。重新声明不会引入新变量；它只是给原始变量赋予新值。
英文:
The short variable declaration is redeclaring game_ratio.
game_ratio := (scaled_score_1+1.0)/(scaled_score_1+scaled_score_2+2.0) + 1.0*0.5
Use an assignment. Write:
game_ratio = (scaled_score_1+1.0)/(scaled_score_1+scaled_score_2+2.0) + 1.0*0.5
> The Go Programming Language Specification
>
> Short variable declarations
>
> A short variable declaration uses the syntax:
>
> ShortVarDecl = IdentifierList ":=" ExpressionList .
>
> It is shorthand for a regular variable declaration with initializer
> expressions but no types:
>
> "var" IdentifierList = ExpressionList .
>
> Unlike regular variable declarations, a short variable declaration may
> redeclare variables provided they were originally declared earlier in
> the same block with the same type, and at least one of the non-blank
> variables is new. As a consequence, redeclaration can only appear in a
> multi-variable short declaration. Redeclaration does not introduce a
> new variable; it just assigns a new value to the original.
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