How to attach a string on php variable

I am trying to attach a string on php variable this is my code

if ($tipy = "2"){
        $username = "dr_" + $username;
    }

and output to be dr_James

But this doesnt work gives me result as 0.

>Solution :

You should use a dot.

if ($tipy = "2"){
        $username = "dr_" . $username;
    }

See php documentation
https://www.php.net/manual/de/language.operators.string.php