What methods can be used to determine if a variable exists in your code?

In PHP, there are several ways to check if a variable exists:

• isset($var): returns true if the variable exists and is not null.
• empty($var): returns true if the variable does not exist or its value is considered empty (e.g., 0, '', null, false, empty array).
• array_key_exists('key', $array): to check if a key exists in an array.
• Using the get_defined_vars() function to get all defined variables.

Example:

if (isset($myVar)) {
    echo "Variable exists and is not null.";
} else {
    echo "Variable does not exist or is null.";
}

It is important to remember that isset does not consider a variable existing if it is null.