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

In PHP the (!!) operator only returns the true value of a variable or expression. To explain in very simple terms, the first NOT operator (!) negates the expression. The second NOT operator (!) negates the expression again, yielding the previously existing truth value. The

(!!) operator is returned as a Boolean function. If !! is used in an expression, the true value is true and the false value is false; the Boolean value does not change.

By using the double NOT (!!) operator, it improves the readability of the code and ensures that true and false values ​​are strictly boolean data types.

Example:

<?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>"; 
?>

Output:

##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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