What does a slash do to a string with a dot in php?

Question

If $GLOBALS['filefolder'] = 13.pressrum How come

$filefolder = '/'+$GLOBALS['filefolder'];
echo $filefolder

output 13

When

$filefolder = $GLOBALS['filefolder'];
echo $filfolder

outputs 13.pressrum

Answer 1

The operator + is numeric / mathematical in PHP. So '/'+$GLOBALS['filefolder']; is equal to 0+13 in your case (php casts both to integer) which actually is 13.

To concatenate use .

$filefolder = '/' . $GLOBALS['filefolder'];
echo $filefolder

Answer 2

A + adds two numbers as in 1+1. So if you use it to concatenate two strings, they get converted to integers internally and thus the result is 13. A dot (.) concatenates two string. So you have to write $filefolder = '/'.$GLOBALS['filefolder'];

You probably confused it with JavaScript, where + is used to concatenate strings (and also for adding numbers, but that's another topic...).