pl sql short code

need small code for this
a-procedure to add new student it take std_id and phone and paramter
if will start from 1000 and increasse +1 for new added emp

exception when enter phone already exist it must display message phone number already used

=============
b- prodeure to add new material to courses
using exeption course not added
lenght of course code c_no = 6 like 101PRG
======
C-PROCEDURE TO ADD course for student to read std_id and c_id
mark to be empty

using exception
s_id is correct and c_no is correct befroe add student
s_id not registered before for same course id c_no

d-procedure to add mark for s_id
select s_id,c_id,mark
exception student must be regitered to this course
mark between 0 and 100

h-

display s_id ,mark paarmter is s_id and c_id
return pass if mark more than 60 or display fail

exception if mark is not enterned then message not entered