为什么 html br 换行标记在此代码中不起作用？

Question

谁能告诉我为什么我的 php 换行符不起作用（回显）？

我知道我可以用不同的方式编写代码来使换行符起作用，但我想知道这背后的原因？

<?php

    $var1 = 3;

    echo "Addition = "       . $var1 += 3 . "<br>";
    echo "Subtraction = "    . $var1 -= 3 . "<br>";
    echo "Multiplication = " . $var1 *= 3 . "<br>";
    echo "Division = "       . $var1 /= 3 . "<br>";

?>

Answer 1

可以使用逗号，

echo "Addition = " . $var1 += 3 , "<br>";
echo "Subtraction = " . $var1 -= 3 ,"<br>";
echo "Addition = " . $var1 *= 3 , "<br>";
echo "Addition = " . $var1 /= 3 ,"<br>";

或者用括号括起来：

echo "Addition = " . ($var1 += 3) . "<br>";
echo "Subtraction = " . ($var1 -= 3) ."<br>";
echo "Addition = " . ($var1 *= 3) . "<br>";
echo "Addition = " . ($var1 /= 3) ."<br>";

否则 3 数字与   连接。

Answer 2

您的 PHP 表示：

echo "Addition = " . $var1 += (3 . "<br>");
echo "Subtraction = " . $var1 -= (3 ."<br>");
echo "Addition = " . $var1 *= (3 . "<br>");
echo "Addition = " . $var1 /= (3 ."<br>");

而 number + 3 . ' ' 是 number + (int)(3 . ' ') 即 number + 3。由于重新输入数字（转换为数字），现在不存在  。

用括号括住方程式。

echo "Addition = " . ($var1 += 3) . "<br>";
echo "Subtraction = " . ($var1 -= 3) ."<br>";
echo "Addition = " . ($var1 *= 3) . "<br>";
echo "Addition = " . ($var1 /= 3) ."<br>";

Answer 3

试试这个..

“。”用于 php 变量连接而不是数字

<?php


$var1 = 3;

echo "Addition = ". ($var1 += 3) ."</br>";
echo "Subtraction = ". ($var1 -= 3) ."</br>";
echo "Addition = ". ($var1 *= 3) ."</br>";
echo "Addition = ". ($var1 /= 3) ."</br>";

?>

Answer 4

试试这个方法。

 <?php
$var1 = 3;

echo "Addition =" . ($var1 += 3 ).'<br>';
echo "Subtraction =" . ($var1 -= 3).'<br>';
echo "Addition =" . ($var1 *= 3 ).'<br>';
echo "Addition =" . ($var1 /= 3 ).'<br>';

?>

Answer 5

发生这种情况是因为类型转换问题。 3 . " " 将在执行操作时转换为数字。包裹内部 () 以便先执行操作然后连接。

echo "Addition = " . ($var1 += 3) . "<br>";
echo "Subtraction = " . ($var1 -= 3) ."<br>";
echo "Addition = " . ($var1 *= 3) . "<br>";
echo "Addition = " . ($var1 /= 3) ."<br>";

Answer 6

看来我必须清理这里的一些东西。

让我们看一下 operator precedence，它说：

. 的优先级高于 +=、-=、*=、/=
. 左结合
=,+=,-=,*=,/=是右结合
我们也看看手册底部的注释：

Note: Although = has a lower precedence than most other operators, PHP will still allow expressions similar to the following: if (!$a = foo()), in which case the return value of foo() is put into $a.

意味着即使是 tough = 也比 . 优先级低，它首先被评估。如果你这样做，你也可以看到这个：

$xy = "HERE";
echo "I am " . $xy = "NOT HERE";

现在你会认为 . 比 = 有更高的优先级并且会先被评估，但是从手册中的注释来看，赋值是第一位的，你最终得到这个:

echo "I am " . ($xy = "NOT HERE");

输出：

I am NOT HERE

因此，如果我们将所有这些信息放在一起，我们可以说，作业首先被评估，但它是正确的关联。意思是：

$var1 = 3;

echo "Addition = "    . ($var1 += 3 . "<br>");
echo "Subtraction = " . ($var1 -= 3 . "<br>");
echo "Addition = "    . ($var1 *= 3 . "<br>");
echo "Addition = "    . ($var1 /= 3 . "<br>");

所以这段代码将以这样的形式结束：

echo "Addition = "    . ($var1 += "3<br>");
echo "Subtraction = " . ($var1 -= "3<br>");
echo "Addition = "    . ($var1 *= "3<br>");
echo "Addition = "    . ($var1 /= "3<br>");

然后通过算术运算符得到 convert to an integer 我们最终得到：

echo "Addition = "    . ($var1 += 3);
echo "Subtraction = " . ($var1 -= 3);
echo "Addition = "    . ($var1 *= 3);
echo "Addition = "    . ($var1 /= 3);

赋值完成后，对连接进行求值，如下所示：

echo "Addition = "    . 6;
echo "Subtraction = " . 3;
echo "Addition = "    . 9;
echo "Addition = "    . 3;

有了这个你最终得到这个输出：

Addition = 6Subtraction = 3Addition = 9Addition = 3

现在如何解决这个问题？只需将您的作业括在括号中，这样   标签就不会进入作业。例如

echo "Addition = "       . ($var1 += 3) . "<br>";
echo "Subtraction = "    . ($var1 -= 3) . "<br>";
echo "Multiplication = " . ($var1 *= 3) . "<br>";
echo "Division = "       . ($var1 /= 3) . "<br>";
                         //^          ^ So the br tag doesn't get in the assignment of the variable.

为什么 html br 换行标记在此代码中不起作用？

Why doesn't the html br break line tag doesn't work in this code?

html

php

operator-precedence