How to properly get a return value from a PHP function?

Question

The code snippet below generates '12290' from the second echo output but the third one is still zero.

How do I get a proper return value from mytest() function?

$testId = 0;
echo 'first: ' . $testId . '<br>';

function mytest($postId) {
    if (get_post_type($postId) === 'artist') {
        $testId = $postId;
    }
    echo 'second: ' . $testId . '<br>';
    return $testId;
}

mytest(12290);
echo 'third: ' . $testId . '<br>';

Answer 1

You forgot to assign the return value to the variable again.
It should be this:

$testId = 0;
echo 'first: ' . $testId . '<br>';

function mytest($postId) {
    if (get_post_type($postId) === 'artist') {
        $testId = $postId;
    }
    echo 'second: ' . $testId . '<br>';
    return $testId;
}

$testId = mytest(12290);
echo 'third: ' . $testId . '<br>';

Answer 2

Instead of:

mytest(12290);
echo 'third: ' . $testId . '<br>';

Try:

echo 'third: ' . mytest(12290) . '<br>';