replace every second comma of string using php

Question

I have a string of that displays like this:

1235, 3, 1343, 5, 1234, 1

I need to replace every second comma with a semicolon

i.e.

Answer 1

Try this:

$s = "1235, 3, 1343, 5, 1234, 1";
$pcs = explode(',', $s);

$flag = false;
$res = '';
foreach ($pcs as $item) {
    if (!empty($res)) {
        $res .= $flag ? ',' : ';';
    }
    $flag = !$flag;
    $res .= $item;
}
die($res);

It outputs:

1235, 3; 1343, 5; 1234, 1