What is the purpose of using isset() in PHP and how can it help prevent undefined variable notices?

When working with variables in PHP, it's common to encounter undefined variable notices if a variable has not been set before being used. This can lead to unexpected behavior or errors in your code. Using isset() in PHP helps prevent these notices by checking if a variable is set before trying to access its value. This function returns true if the variable is set and not null, and false otherwise.

// Using isset() to prevent undefined variable notices
$variable = isset($someVariable) ? $someVariable : null;

// Now $variable will either contain the value of $someVariable if it is set, or null if it is not set