What are mutable variables in PHP? How to understand mutable variables?

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Variable variables:

$s1 = "abe";
//这是一个变量，里面存储的是字符串"abe"
$abc=10,
echo S$s1;
//??输出10

Understanding:

1, in php , an "S" is always followed by a variable name!

2. Here, the name of the variable output by echo (identified by the -th S) is: $sl, I"abe "

3, so what is output here is sabc, which is 10

4. This variable form in which "$" appears continuously is the so-called "variable variable"

The code is as follows:

<?php
$s1 = &#39;abc&#39; ;
//这是一个变量，里面存储的是字符串"abc"
$abc= 10;
//
echo $$s1;   //???,输出10
?>

The running results are as follows:

The code is as follows:

The following demonstrates the flexibility of "variable variables":
The so-called variable variables actually mean that the name of the variable can be "dynamically changed" to obtain different data values

$v1 = 1;
$v2 = 12;
$v3 = 33;
$v4 = 44;
$v5 =115;
//求这5个变量的和:
//其他语言，只能“一个一个”加起来。
$sum = 0; //用于存储总和
for($i = 1; $i <= 5; $i++){
$v ="v".$i; //这里，结果其实只是一个“字符串”，比如"v1","v2" ...
$sum += $$v;
}
echo "<br />sum = $sum";
?>

Running results As follows:

Recommended learning: php video tutorial

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