如何从字符串中添加数字

I want to add number from my string. this is my string

$formula = 'IF(B15="","",IF(ISNUMBER(A14),A14+1,IF(ISNUMBER(B3),B3+1,1)))';

i want add number if before the number is alphabet. for example i want to make B15 to B16 ini my string.. this my loop

$jum = strlen($formula);
for($i = 0; $i < $jum; $i++){
    if(ctype_alpha($formula[$i]) && ctype_alnum($formula[$i+1])){
        $temp_formula[$i+1] += 1;
    }
}

You can do this with preg_replace_callback. Use this regex, which looks for a symbol of the form <letter><digits> between word boundaries:

\b([A-Z])(\d+)\b

and then in the callback the second group's value can be incremented:

$formula = 'IF(B15="","",IF(ISNUMBER(A14),A14+1,IF(ISNUMBER(B3),B3+1,1)))';
echo preg_replace_callback('/\b([A-Z])(\d+)\b/', function ($m) {
    return $m[1] . (1 + $m[2]);
}, $formula);

Output:

IF(B16="","",IF(ISNUMBER(A15),A15+1,IF(ISNUMBER(B4),B4+1,1)))

Demo on 3v4l.org

Update

To use an external variable in the callback (as described in the comments), edit the code like this:

$formula = 'IF(B15="","",IF(ISNUMBER(A14),A14+1,IF(ISNUMBER(B3),B3+1,1)))';
$tambah = $adding + ($rekord*$highest);
echo preg_replace_callback('/\b([A-Z])(\d+)\b/', function ($m) use ($tambah) {
    return $m[1] . ($tambah + $m[2]); 
}, $formula);