PL/SQL question, Please help

Hello All:

     In a PL/SQL procedure, I was tring to use a "in" statment in a select
     query. But for some reason it didn't work right. Here is my code:

     SQL> declare
       2       v_addtype  varchar2(100) := '''m'',''mb''';
       3      i number;
       4  Begin
       5       SELECT count(*) into i
       6       FROM  UserAddr
       7       WHERE addrtype in (v_addtype);
       8       DBMS_OUTPUT.put_line('##### count = ' || i||' #####' );
       9  End;
      10  /


     ##### count = 0 #####


     PL/SQL procedure successfully completed.

     But if I directly use the value instead of using the variable
     "v_addtype". It works fine:

      SQL> declare
       2       i number;
       3  Begin
       4       SELECT count(*) into i
       5       FROM  UserAddr
       6       WHERE addrtype in ('m','mb');
       7       DBMS_OUTPUT.put_line('##### count = ' || i||' #####' );
       8  End;
       9  /


     ##### count = 265 #####


     PL/SQL procedure successfully completed.

     What was wrong in my first statement? 

     Great thanks for any help.

     Jeff