how to check if a verible is defined after a form post code example

Example 1: php see if undefined

if (isset($variable)) { /* do something */ };

Example 2: isset in php

//with new features in new PHP versions like 7
//you can simplify writing of isset in the following way,
//old way of isset to display name if name variable is not null
echo isset($name) ? $name : "no name"
 //new and simple way with null coalescing operator
echo $name ?? "no name"