Why the Code doesn't change the type?

Question

I want to change a string into a float or null.

https://code.sololearn.com/wfKlHjs8H6Xz/?ref=app

Answer 1

you never changed $text
in validateFloat you should change last line to
$text= floatval($text);

Answer 2

thx your right one mistake fixed :D
but unset doesn't work
$text = null;
also doesn't work

Answer 3

ah ok i have fixed the problem
$text = NULL;
unset doesnt work in this scope