How do I negate this if/else comparison to just if? [closed]

问题

I'm trying to set the class hidden, unless two factors are met. Currently, I'm using the code below:

<?php 
if (isset($_POST['prerequisite']) && $form == "CheckingIn")
{

}
else
{
    echo "hidden";
}
?>

How can I fix this to just be an if statement instead of an if/else?

回答1:

Negate the expression; use the "NOT" logical operator:

if (!(isset($_POST['prerequisite']) && $form == "CheckingIn")) { echo "hidden"; }

(notice the ! symbol)

Read more here: http://php.net/manual/en/language.operators.logical.php

来源：https://stackoverflow.com/questions/18247639/how-do-i-negate-this-if-else-comparison-to-just-if