Indirect reference of variables, connection string and connection assignment operator of PHP entry variables_PHP tutorial

【1】Indirect reference of variable:

<?php 
 $a = 'b';
 $$a = '123'; 
 echo $b; 
?>

The above output is 123

We can see that there is an extra $ in the second line of code, and the variable is accessed through the specified name. The specified name is stored in $a('b'), and the value of this variable $b is changed to 123. Therefore, such a variable of $b is created and assigned.

You can increase the number of references arbitrarily by adding an additional $ mark in front of the variable.

【2】Concatenate strings: Use the concatenation operator, that is, the period (.) in the English state, to concatenate the strings into a merged new string.

<?php 
	$a = 'PHP5' ; 
	$b = '功能强大' ; 
	echo $a.$b; 
?>

In order to let us understand the connection string better, we changed it based on the above example and turned it into something like this (PHP5: Powerful 2014)

In this example we see quotes, spaces and numbers added. Below we will use two methods to write, and you will find out the specific differences yourself:

<?php 
	$c = $a.': '.$b.' 2014';
	$c = $a.': '.$b.' '.2014;
?>

【3】Connection assignment operator: If you only connect one value to another value, you can use the connection assignment operator (.=). The following two statements are equivalent:

<?php 
	$title = $title . $subtitle; 
	$title .= $subtitle; 
?>

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