Got you. Here is where you got it wrong. PHP is a loosely typed language, means empty array evaluates to FALSE. So, if($_POST) will return true only if the information was submitted.
Again you mistaken here. There are billions of while codes around, each happily terminated with empty fetch. thanks to the same loose typing and type casting. Just try it and see 
I am eager to know where did you get such peculiar ideas? Is it some online tutorial or something? Or just different language in background?