PHP - If statements with || - Need help

Question

I don't understand why this doesn't work.

if I run this, it redirects me to the protected.php.

Also, in your experience. Is this the best way to check this?

function admin_protect($user_ok, $log_userlevel) {
    if ($user_ok === true) { //This is checking to make sure the user is logged in - just in case.
        if ($log_userlevel !== '7' || $log_userlevel !== '8') {
            header('Location: protected.php');
            exit();
        }
    }
}

if I run it like this then it works.

function admin_protect($user_ok, $log_userlevel) {
    if ($user_ok === true) {
        if ($log_userlevel !== '7') {
            header('Location: protected.php');
            exit();
        }
    }
}



//or like this

function admin_protect($user_ok, $log_userlevel) {
    if ($user_ok === true) {
        if ($log_userlevel !== '8') {
            header('Location: protected.php');
            exit();
        }
    }
}

Answer 1 · 2014-09-27T02:50:43Z

September 27, 2014 2:50am

Put && instead of || and use != instead of !==

Answer 2 · 2014-09-27T08:35:09Z

September 27, 2014 8:35am

I believe you're experiencing what's called "short circuiting." In the case of using ||, the system doesn't check to see if both are true. It gets to the first, checks $login_userlevel !=='7', and if that returns true it doesn't continue to the next condition because a true value has already been found. In that case, if $login_userlevel !== '7' always returns true, then $login_userlevel !== '8' will never be checked. In this case, there is a chance that a value of '8' could slip through, so it would make more sense to use &&. Using && says I want to make sure both conditions are true before executing the code below.

Answer 3 · 2014-09-28T17:43:39Z

September 28, 2014 5:43pm

The first very important thing to realize is that multiple conditionals do not relate to each other at all.

This statement

<?php
($log_userlevel !== '7' || $log_userlevel !== '8')

if the user is not level 7 continue OR if the user is not level 8 continue.

As Ricardo Hill-Henry mentioned, PHP will work through the statements in order.

If the user is level 8, the first statement will pass, because this user is not level 7 and the 'if' block will be run. The same applies if the user is level 8.

You need to use an && statement, because both your conditionals need to be true to pass. i.e. the user should not be level 7 AND should not be level 8. Using && means both statements need to return true before the if block can be run.

Now, this is so because you're avoiding a negative. If you were to be choosing an action which depended on the user being 7 or 8, then && wouldn't make sense - because a user can only be one level.

<?php
($log_userlevel == '7' && $log_userlevel == '8') {
    // This code won't run
}

In this case, you would be right to check for OR

<?php
($log_userlevel == '7' || $log_userlevel == '8') {
    // Level 7 or level 8 users would be redirected.
}

If you're testing for the negative - i.e. only people NOT level 7 or 8 get redirected

<?php
($log_userlevel !== '7' && $log_userlevel !== '8') {
    // Users who are both NOT level 7 AND NOT level 8 will be redirected.
}

Here you're testing for a negative OR

<?php
($log_userlevel !== '7' || $log_userlevel !== '8') {
    // Users who are NOT level 7 (i.e. could be level 8 will get redirected)   
    // Users who are NOT level 8 (i.e. could be level 7 will get redirected)

}

Work through this enough times and it should make a bit more sense ;)

Welcome to the Treehouse Community

Looking to learn something new?

Andrew McCombs

Andrew McCombs

PHP - If statements with || - Need help

3 Answers

Tariq Naeem

Tariq Naeem

Ricardo Hill-Henry

Ricardo Hill-Henry

Andrew McCombs

Andrew McCombs

thomascawthorn

thomascawthorn