How can the issue of declaring a class or function multiple times be resolved in PHP?

When declaring a class or function multiple times in PHP, it can lead to a "cannot redeclare" fatal error. To resolve this issue, you can first check if the class or function exists before declaring it using the `class_exists()` or `function_exists()` functions. If the class or function does not exist, then go ahead and declare it.

if (!function_exists('myFunction')) {
    function myFunction() {
        // function implementation
    }
}