Hi Hrishy,
I changed it, reran the function, tested it. It is still would not work.

SQL> CREATE OR REPLACE FUNCTION trina_verify_function
2 (username varchar2,
3 password varchar2,
4 old_password varchar2)
5 RETURN boolean IS
6 n boolean;
7 m integer;
8 differ integer;
9 isdigit boolean;
10 ischar boolean;
11 ispunct boolean;
12 isupper boolean;
13 digitarray varchar2(20);
14 punctarray varchar2(25);
15 chararray varchar2(52);
16 regular_expr varchar2(50);
17
18 BEGIN
19 digitarray:= '0123456789';
20 chararray:= 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
21 punctarray:='!"#$%&()``*+,-/:;<=>?_';
22 regular_expr:= '[A-Z]';
23 if regexp_instr(password,regular_expr) > 0 THEN
24 dbms_output.put_line('it has one upper case letter');
25 end if;
26
27 -- if everything is fine retrun true.
28 RETURN(true);
29 END;
30 /

Function created.

SQL> alter user trina identified by trina_7777777777;

User altered.

SQL> alter user trina identified by trina_B77777777;

User altered.