How can the issue of undefined variables, such as $id in the provided script, be resolved in PHP programming?

The issue of undefined variables like $id in PHP can be resolved by first checking if the variable is set using isset() function before using it in the code. This helps to avoid errors and warnings when the variable is not defined. Another approach is to initialize the variable with a default value if it is not set, ensuring that it is always defined before being used in the script.

// Check if $id is set before using it
if(isset($id)) {
    // Use $id in the code
    echo "ID: " . $id;
} else {
    // Initialize $id with a default value
    $id = 0;
    echo "ID: " . $id;
}