$_POST echoing 0 when containing strings

Question

I made a basic HTML form working with post (it's a login form). The form itself works great, but when I try to work with the information contained in $_POST it goes wrong.

<?php
        // case : nothing submitted
        if (!isset($_POST['submit'])) {
        ?>
            <div class="login">
                <form action="<?=$_SERVER['PHP_SELF']?>" method="post">
                    <p>Login</p>
                    <input type="text" id="username" placeholder="Username" name="username" />
                    <input type="password" id="password" placeholder="Password" name="password" />
                    <button name="submit">Submit</button>
                </form>
            </div>
        <?php
        // case : input form submitted
        } else {
            check_credentials();            
        }
?>

The problem is, it works fine when I do this ( above check_credentials() : echo $_POST['username']; echo $_POST['password'];

But when I do this : echo $_POST['username'] + " " + $_POST['password']; It echoes 0. As check_credentials() is a function that connects to my DB, the request isn't executed. Does someone have any idea of the possible cause ?

Greetz !

Answer 1

You must use dots when concatenating in PHP. You probably "took" pluses from JS.

It should look like in this example:

    <?php
    $a = "Hello ";
    $b = $a . "World!"; // now $b contains "Hello World!"
    $a = "Hello ";
    $a .= "World!";     // now $a contains "Hello World!"
    ?>

And your example, if the variables are good:

  echo $_POST['username']." ".$_POST['password'];