java for循环不起作用 [英] java for loop not working

问题描述

我希望这不是一个愚蠢的问题，但是我已经查找了所有可以找到的示例，并且看起来我仍然拥有正确的代码，但是仍然无法正常工作...我输入了一个数字，然后继续操作到下一行代码，而不是循环.我正在用它来填充用户输入数字的数组.感谢您的帮助，谢谢.

I hope this isn't a stupid question but I have looked up every example I can find and it still seems like I have this code right and it still isn't working... I enter one number and it moves on to the next line of code instead of looping. I'm using this to fill an array with user input numbers. I appreciate any help, thanks.

for(i=0; i<9; i++);
{  
    System.out.println ("Please enter a number:");  
    Num[i] = keyboard.nextDouble();  
    Sum += Num[i];      
    Product *= Num[i];      
}   

推荐答案

for循环末尾的;被视为空语句，等效于for循环的空块.编译器将您的代码读取为:

The ; at the end of the for loop is taken as an empty statement, the equivalent of an empty block for your for-loop. The compiler is reading your code as:

int i;
....
for(i=0; i<9; i++)
    /* no-op */;

/* inline block with no relation to for-loop */
{  
    System.out.println ("Please enter a number:");  
    Num[i] = keyboard.nextDouble();  
    Sum += Num[i];      
    Product *= Num[i];      
} 

删除;以获得预期的行为.

Remove the ; to get your intended behavior.

如果不需要循环外的i，则可以在for语句内移动其声明.

If you don't need the i outside of the loop, you could move its declaration within the for statement.

for(int i=0; i<9; i++)
{
   // `i` is only usable here now
}
// `i` is now out of scope and not usable

在出现错误的分号;时使用此语法会产生编译错误，该错误会提前提醒您错误的;.编译器会看到以下内容:

Using this syntax when the erroneous semicolon ; was present would have produced a compile error that would alerted you to the erroneous ; earlier. THe compiler would see this:

for(int i=0; i<9; i++)
    /* no-op */;

/* inline block with no relation to for-loop */
{  
    System.out.println ("Please enter a number:");  
    Num[i] = keyboard.nextDouble();     // compile error now - `i` is out-of-scope
    Sum += Num[i];      
    Product *= Num[i];      
} 

这是一个示例，为什么在可能的情况下最好限制变量的范围.

This would be an example why it is good practice to limit the scope of variables when possible.

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