PHP random number generation class

<? PHP
Class getrandstrclass {
Function getcode ($ length = 32, $ mode = 0 ){
Switch ($ mode ){
Case '1 ':
$ STR = '000000 ';
Break;
Case '2 ':
$ STR = 'abcdefghijklmnopqrstuvwxy ';
Break;
Case '3 ':
$ STR = 'abcdefghijklmnopqrstuvwxy ';
Break;
Case '4 ':
$ STR = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxy ';
Break;
Case '5 ':
$ STR = 'abcdefghijklmnopqrstuvwxyz1234567890 ';
Break;
Case '6 ':
$ STR = 'abcdefghijklmnopqrstuvwxyz1234567890 ';
Break;
Default:
$ STR = 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz1234567890 ';
Break;
}
$ Randstring = '';
$ Len = strlen ($ Str)-1;
For ($ I = 0; $ I <$ length; $ I ++ ){
$ Num = mt_rand (0, $ Len );
$ Randstring. = $ STR [$ num];
}
Return $ randstring;
}
}
/* Usage
$ Code = new getrandstrclass ();
$ Length = 4;
$ Mode = 0;
$ STR = $ code-> getcode ($ length, $ mode );
Echo $ STR;
$ Code = NULL;
*/
?>