> Even if the form was submitted and $_POST is not empty, you should check
> every value if it exists before you use it.



why?

I'm using them this way: if I receive the values I put them in the
value field of the form, if I don't receive data, the field appears
empty.



> You could also have a look at the extract() function, if you want to
> convert the array into single variables. I don't consider that really
> necessary, but anyway.



I considered not using it because the PHP manual says it is not a good
idea for $_GET, $_POST, etc.