C风格的循环与Perl循环（在Perl中） [英] C-style loops vs Perl loops (in Perl)

问题描述

我觉得有一些我没有得到关于Perl的循环机制。

据我了解，

  
 
 
 
 
 
 
 $ p 
在功能上等价于：
  for（my $ i = 0; $ i <= $＃arr; $ i ++）{..} 
  
但是，在我的代码中，它们的运行方式似乎有一些细微的差别。特别是他们决定何时终止的时间。例如：
 
 
假定@arr是用一个变量初始化的。 
 
 
 
这两个块应该做同样的事情吗？ 
 
 
  for我的$我（0 .. $＃ARR）
 {
如果（一些条件恰好是真的）
 {
 push（@arr，$ value）; 
 
 
 
 
 
 
 
 
 
 
 
 $ b （$ my $ i = 0; $ i< = $＃arr; $ i ++）
 {
 if（某些条件碰巧是true）
 {
 push（@arr，$ value）; 
 
 
 
 
 
 
 
然而，即使一个新的值被推送在这两种情况下，第一个循环只会在一次迭代后停止。 
 
 
 
这是否应该发生？如果是的话为什么 
 
 
 编辑：谢谢你所有的答案，我知道我可以用其他循环机制完成同样的事情。当我问是否还有另一种语法时，我正在专门讨论使用for。显然没有。作为语法来做我想要的是已经实现了C风格。我只是问，因为我被告知避免c风格，但我仍然喜欢我的循环。 
解决方案
  $ i <= $＃arr 而（0.. $＃arr）在任何循环之前都会被计算一次。
 
 
同样，第一个代码不会看到对 @arr 尺寸的更改。
 
I feel like there is something I don't get about perl's looping mechanism. 

It was my understanding that 
for my $j (0 .. $#arr){...} 
was functionally equivalent to:
for(my $i=0; $i<=$#arr; $i++){..}
However, in my code there seems to be some slight differences in the way they operate. specifically, the time in which they decide when to terminate. for example:

assume @arr is initialized with one variable in it.  

These two blocks should do the same thing right?
for my $i (0 .. $#arr)
{
    if(some condition that happens to be true)
    {
        push(@arr, $value);
    } 
} 
and
for (my $i=0; $i<=$#arr; $i++)
{
    if(some condition that happens to be true)
    {
        push(@arr, $value);
    } 
} 
In execution however, even though a new value gets pushed in both cases, the first loop will stop after only one iteration. 

Is this supposed to happen? if so why?  

EDIT: Thank you for all of your answers, I am aware I can accomplish the same thing with other looping mechanisms. when I asked if there was a another syntax, I was specifically talking about using for. Obviously there isn't. as the syntax to do what I want is already achieved with the c style. I was only asking because I was told to avoid the c style but i still like my for loops. 
解决方案
$i<=$#arr is evaluated before each loop while (0 .. $#arr) is evaluated once before any loop.

As such, the first code doesn't "see" the changes to the @arr size.

                        
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