为什么html br break行标记在这段代码中不起作用？

Question

有人可以告诉我为什么我的php行不能正常工作（回声）吗？

我知道我可以用不同的方式编写代码来使换行工作，但我想知道背后的原因吗？

<?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

好像我必须在这里清理一些东西。

让我们看看operator precedence，其中说：

1. .的优先级高于+=，-=，*=，/=
2. .是左关联的
3. =，+=，-=，*=，/=是正确的关联

4. 我们还会看一下手册底部的注释：

     

   注意：   虽然 =的优先级低于大多数其他运算符，但PHP仍然允许使用类似于以下的表达式：if（！$ a = foo（）），在这种情况下，foo（）的返回值为投入$ a。

意味着即使强硬=的优先级低于.，也会先评估它。如果您执行以下操作，也可以看到此内容：

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

现在您认为.的优先级高于=，并且会先评估，但从手册中的说明开始，分配是第一个，您最终得到的结果是：< / p>

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，首先评估分配，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>");

所以这段代码最终会出现在：

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我们最终得到这个：

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

分配完成后，会对连接进行评估，如下所示：

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

这样你就得到了这个输出：

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




现在如何解决这个问题？只需将作业包装在括号中，以便<br>标记不会进入作业。 E.g。

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.

Answer 2

由于类型转换问题，这种情况正在发生。在执行操作时，3 . "<br>"将转换为数字。包裹内部()，以便首先执行操作，然后执行连接。

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

Answer 3

您可以使用逗号

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号码会与<br>连接。

Answer 4

您的PHP意味着：

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

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

在方程式周围使用括号。

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

Answer 5

试试这个..

“”。用于php变量来连接数字

<?php


$var1 = 3;

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

?>

Answer 6

试试这种方式。

 <?php
$var1 = 3;

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

?>