function extract_only_characters($s) {
$len = strlen($s);
$characters = "";
for ($i = 0; $i < $len; $i++) {
$ch = $s[$i];
if (ctype_alpha($ch)) {
$characters = $characters . $ch;
}
}
return $characters;
}
$s = "c++14@vb.NET&%java*() php <>/python 3.7.3";
echo extract_only_characters($s);
/*
run:
cvbNETjavaphppython
*/