How to use double NOT (!!) operator in PHP? (code example)

In PHP we often use the "!" operator. A single "!" means negation, so what is the role of double "!", that is, the double no (!!) operator? The following article will introduce you to the double no (!!) operator and introduce how to use the double no (!!) operator in PHP. I hope it will be helpful to you. [Video tutorial recommendation: PHP tutorial]

##PHP (!!) operator

<?php 
// 声明变量并初始化它
$a1 = 2; 
$a2 = 0; 
$a3 = 1; 
$b1 = false; 
$b2 = true; 
// 使用双非（!!）运算符
$a1 = !!$a1; 
$a2 = !!$a2; 
$a3 = !!$a3; 
$b1 = !!$b1; 
$b2 = !!$b2; 
// 输出变量a的值
echo "$ a1=".$a1."<br>"; 
echo "$ a2=".$a2."<br>"; 
echo "$ a3=".$a3."<br>"; 
echo "$ b1=".$b1."<br>"; 
echo "$ b2=".$b2."<br>"; 
?>

##Logical NOT (!) operator and double negation in PHP Differences between (!!) operators: The non-(!) operator is the negation of the Boolean value of the data. For example, define a Boolean value $a = True, and then impose the NOT operator on it, !$a will be False; it's about the logical NOT or negation operator.

However, the double NOT (!!) operator only returns a Boolean cast or a true value; therefore, the output of !!$ is always true.

Example:

<?php 
header("content-type:text/html;charset=utf-8");
$t = 10; 
// 检查条件
if ($t !== 10) 
    echo "这是逻辑非（!）运算符"; 
elseif (!!$t) 
    echo "这是双非（!!）运算符"; 
else
    echo "完成"; 
?>

Output:

这是双非（!!）运算符

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