The PHP function return value can return a bool value and return other values as well. This function can also determine the true and false

function luhn_checker($card_num,$sum){    ....    return ?;

That is, you can return a bool value and return a value such as $sum, and the function needs to determine whether it is true or false

if(luhn_checker($card_num)){ }

Reply content:

function luhn_checker($card_num,$sum){    ....    return ?;

That is, you can return a bool value and return a value such as $sum, and the function needs to determine whether it is true or false

if(luhn_checker($card_num)){ }

PHP can use arrays and lists to retain the word to return multiple values, but still need to judge a single line ...

function luhn_checker($card_num, $sum) {    return array(true, $sum);}list($ret, $sum) = luhn_checker($card_num, $num);if($ret) ...

Append: The kv array method mentioned in the question comment can also be solved by a list into multiple variables, the order of the Untied values is the same as the order of the definition.

A variety of types is best to use = = = to judge ...

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