从字符串中保存数字

Question

I'm looking to store all number's that occur alone in a string. The integers must occur on their own and be surrounded by white space.

Here's what I mean:

Input

blah 5 blah bl3h 555 blah 123 blah a2b3 5030a

Expected Output

[5], [555], [123]

Here's my attempted iterator that seems to group the current word correctly but adds nothing to the array

//$a = String
function numberReturn($a){

    $currWord;

    $numberArray = array();

    //Loop through string
    for($i = 0; $i < strlen($a); $i++){
        //Keep adding chars to current word
        $currWord .= $a[$i];


        //if white space check if current word is only numeric
        //if only numbers add it to array
        //when added, clear current word
        if(ctype_space($a[$i])){
            if(is_numeric($currWord)){
                $numberArray[] = $currWord;
            }
            $currWord = "";
        }
    }
    return $numberArray;
}

Answer 1

Unless you specifically need to use a loop, you can explode on space and filter out every substring that isn't made of digits.

$numbers = array_filter(explode(' ', $string), 'ctype_digit');