How to formulate 'if not' in php?

Pedroski55 · December 21, 2019, 3:47am

My students need to enter their class name on my webpage, because that locates them in my excel tables. Some of them enter weird and wonderful things there!

I am not too clear on how to formulate ‘if not’ in php. So far I have:

$classes = array('18BE1', '18BE2', '18BE3');

$class = $_POST['class'];
//First, check if the student entered the class name correctly
       if(in_array($class, $classes)) = false {
       echo " 错误：班号不对！ Class name wrong! <br> ";
       echo " Please enter the correct class name. <br>";
       echo " Your details could not be sent. <br>";
       echo " 反回再次试一试！ Try again!";
	exit;
}

Will that work? In Python I would just write:

if $class not in $classes:

phdr · December 21, 2019, 4:14am

You should have a select/option menu consisting of the same choices that are in the $classes array, so that only a valid choice can be made.

No, due to bad syntax. The in_array() call is correct, but the if() comparison has two problems, that will both disappear once you simply test the boolean result from the in_array() directly. 1) The closing ) for the if( is in the wrong location, and 2) one = is an assignment operator, two == is a comparison operator. The current code is trying to assign a false value, not compare with a false value. However, don’t compare returned boolean values to true/false values. This misses the point of booleans. Just directly use them in an if() conditional test.

To ‘not’ a boolean value, prepend a !

if(!in_array($class, $classes)) { // if not in array
}

Pedroski55 · December 21, 2019, 4:55am

Thanks a lot! Works like a dream!

frankbeen · December 21, 2019, 10:21am

Above answer is 100% correct but In case you dont want to use the exclamation mark then you could write

if(false === in_array($class, $classes)  { // if not in array
}

Watch the === comparison operator. It will ensure that two of the same type will be compared, in this case Boolean values.