What is the difference between if(isset($a)) and if($a) in php? -

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what difference between if(isset($a)) , if($a) or if_exist($a) , if($a) in php?

with $a = false;:

if ($a) {} return false, whereas if (isset($a)) {} return true.

i not know if_exist speak of. :)

edit: please check @utkanos's answer excellent , more expansive explanation. :)


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