php PHP在for循环内嵌套for循环

PHP nesting for loop inside for loop

提问by Dan

Been trying to figure this one out for the last 3 hours and so hard to find any search results for "nesting for loop inside for loop", so I must ask this question and somebody can help clarify, as much of an amateur question this is, will much appreciate any and all help.

在过去的 3 个小时里一直试图弄清楚这个问题，但很难找到“在 for 循环中嵌套 for 循环”的任何搜索结果，所以我必须问这个问题，有人可以帮助澄清，这是一个业余问题，将不胜感激任何和所有帮助。

So I have this block of code underneath, for a beginners looping exercise I found at http://www.w3resource.com/php-exercises/php-for-loop-exercises.phpon question 3 of that page. The end result should be on that page as well.

所以我在下面有这个代码块，对于初学者循环练习，我在http://www.w3resource.com/php-exercises/php-for-loop-exercises.php上找到了该页面的问题 3。最终结果也应该在该页面上。

<?php
    for($a = 1; $a <= 5; $a++) {
        for($b = 1; $b <= $a; $b++) {
            echo "*";
            if($b < $a) {
               echo " ";
            }
        }
        echo "<br />";
    }
?>

It turns out like a triangle shape made up of 15 little *

原来是一个三角形的形状，由 15 个小 *

I am trying to figure out exactly how this works, as even though the site has an answer, I want to understand so I can write things myself instead of copy pasting.

我正试图弄清楚这是如何工作的，即使该网站有答案，我也想了解一下，这样我就可以自己写东西而不是复制粘贴。

Below is what I have been able to make out after reading php.netand also trying to look for a solution on Google.

以下是我在阅读php.net并尝试在 Google 上寻找解决方案后所得出的结论。

So, the $aforloop starts off as true so loop continues onto the $b FORloop, it is true so it will echo *, At this point $bis not < $aas loop is not yet over so the ++have not been added yet and ifstatement is false, so we <br />and re-run loop.

所以，$afor循环开始为真所以循环继续$b FOR循环，它是真的所以它会回声*，此时$b不是< $a因为循环还没有结束所以++还没有被添加并且if语句是假的，所以我们<br />重新- 运行循环。

Second time around. Now $a=2and forloop is still true so it will go on to $bfor loop and echo *. This is where I get confused. The $bhas ++at the end of its statement, so doesn't it mean that after loop 1 $b = 2and ifis still false ?

第二次来了。现在$a=2and forloop 仍然是真的，所以它会继续$bfor loop 和 echo *。这是我感到困惑的地方。将$b有++在发言结束，所以并不意味着该循环1后$b = 2和if仍然是假的？

In my head I keep thinking it should print out like:

在我的脑海中，我一直认为它应该打印出来：

<br />* <br /> * <br />

<br />* <br /> * <br />

instead of this:

而不是这个：

<br />* <br /> * * <br />

<br />* <br /> * * <br />

My conclusion.

我的结论。

1. The $bvalue will reset back to 1 after each loop and repeats itself until ifstatement is false.

1. $b每次循环后该值将重置回 1 并重复自身直到if语句为假。

OR

或者

1. The *that get printed are stored and will be the automatic starting point at the beginning of each loop. I understand that if doing a simple print for a for($i=0;$i<11;$i++)loop will carry the value over, however in my situation, a printed *is not a value, so it shouldn't be carried over to a new loop.

2. 的*是那些获得的印刷被存储并且将在每个循环的开始自动起点。我知道如果为for($i=0;$i<11;$i++)循环做一个简单的打印会携带这个值，但是在我的情况下，打印*的不是一个值，所以它不应该被转移到一个新的循环中。

OR

或者

1. I am just completely off with both my conclusions.

3. 我完全不同意我的两个结论。

Either way, its been confusing me so badly.

无论哪种方式，它都让我非常困惑。

Sorry for long explanation.

抱歉解释太长了。

Thanks.

谢谢。

回答by Hanky Panky

Let's take things one step at a time

让我们一步一步来

Outer Loop

外环

   for($a = 0; $a <= 5; $a++) {
      //inner loop  here
      echo "<br>";  //after the inner loop has executed, start a new line
    }

Start at 0, go up to 5 and do whatever is written inside. Now that means two things will happen for each iteration

从 0 开始，到 5 并执行里面写的任何操作。现在这意味着每次迭代都会发生两件事

1) Inner loop will be executed for every iteration of the outer loop

1) 外循环的每一次迭代都会执行内循环

2) An HTML row break will be printed for every iteration of the outer loop

2) 外循环的每次迭代都会打印一个 HTML 换行符

Now what does the Inner Loopdo?

现在内循环做了什么？

    for($b = 1; $b <= $a; $b++) {
        echo "*";
            if($b < $a) {
                echo " "; // $b<$a means we still have more stars to print on this line
            }
    }

Start at 1, go up to the value of $a, this $a will come from the outer loop and will be 1 for the first run, 2 for second up to 5. And while doing this, print a *; that means for the first time 1 star will be printed because loop will start at 1 and end at 1. For the second time 2 stars, 3rd time three stars and so on.

从 1 开始，一直到 的值$a，这个 $a 将来自外部循环，第一次运行时为 1，第二次运行时为 2，直到 5。在执行此操作时，打印 a *; 这意味着第一次将打印 1 颗星，因为循环将从 1 开始并在 1 处结束。第二次 2 颗星，第三次 3 颗星，依此类推。

Now after printing the star, see if this is the last star that this iteration had to print, if it is not that then print a space so that the next time a star is printed there is a space in between.

现在打印星星后，看看这是否是本次迭代必须打印的最后一颗星星，如果不是，则打印一个空格，以便下次打印星星时中间有一个空格。

That's about it :) Note that your outer loop starts at 1, it should start at 0 to form the required shape correctly.

就是这样 :) 请注意，您的外循环从 1 开始，它应该从 0 开始以正确形成所需的形状。

Now if you are still confused about the $b<$athing, just get rid of it and run your code again and you will notice nothing much has changed except that there are no spaces between the stars and it will be a little easier to understand

现在，如果您仍然对这$b<$a件事感到困惑，只需摆脱它并再次运行您的代码，您会发现除了星星之间没有空格之外没有任何变化，并且会更容易理解

    for($b = 1; $b <= $a; $b++) {
        echo "*";
    }

And oh, ++after a variable means increment its value by 1. In a for loop that means on the next run add 1 to the value of the counter. You can also write it as

哦，++在变量之后意味着将其值增加 1。在 for 循环中，这意味着在下一次运行时将计数器的值加 1。你也可以把它写成

for($a=0; $a<=5; $a=$a+1)      // thats the same as $a++;

If you wanted the value to increment by more than 1 you could say

如果您希望该值增加超过 1，您可以说

for($a=0; $a<=5; $a=$a+2)    // a will be 0 , 2, 4

Fiddle

小提琴