PHP generates random strings (pure numbers and pure letters can be specified)

Example, PHP generates a random string, you can specify whether it is pure numbers, pure letters, or a mixture, and you can specify the length.

//Generate a random string
function rand_zifu($what,$number){
$string='';
for($i = 1; $i <= $number ; $i++){
//Mix letters and numbers
$panduan=1;
if($what == 3){
if(rand(1,2)==1){
$what=1;
} else{
$what=2;
}
$panduan=2;
}
//Only numbers
if($what==1){
$string.=rand(0 ,9);
}elseif($what==2){
//Only letters
$rand=rand(0,24);
$b='a';
for($a =0;$a < ;=$rand;$a++){
$b++;
} bbs.it-home.org
$string.=$b;
}
if($panduan==2)$what=3;
}
return $string;
}
echo rand_zifu(3,10);