IN parameters are used to pass values into the subprogram. but can't be changed.
IN Parameters are really a constant.
IN Parameters work in only one direction from the main program to subprogram.
SQL> create or replace function getArea (i_rad NUMBER)
2 return NUMBER
3 is
4 begin
5 if i_rad is null -- legal
6 then
7 -- i_rad:=10; -- ILLEGAL
8 return null;
9 end if;
10 return 3.14*(i_rad**2); -- legal
11 end;
12 /
Function created.
SQL>