Difference of execution in SQL Developer and SQL *Plus - sqlplus

Question

The following code runs good as expected in SQL Developer without any errors, but when I run the code in SQL*Plus it is throwing an error.
declare
v_num1 integer := '&a';
v_num2 integer := '&b';
v_result number;
begin
v_result := v_num1 / v_num2;
dbms_output.put_line ('v_result: '||v_result);
end;
The error raised is
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at line 2
Please point out where the error I made.

Answer 1

Your SQL*Plus session has substitution variables turned off, so the '&a' is being treated as a literal string, and it isn't prompting you for the value. In a simplified version:
set define off
declare
i integer := to_number('&a');
begin
null;
end;
/
declare
*
ERROR at line 1:
ORA-06502: PL/SQL: numeric or value error: character to number conversion error
ORA-06512: at line 2
To fix it, turn substitution variables back on:
set define &
Then it works:
declare
i integer := to_number('&a');
begin
null;
end;
/
Enter value for a:
If I enter 1:
PL/SQL procedure successfully completed.
You don't need the quotes, or the to_number(), unless you're using group seperators (and then you'd need to supply a format model too). You can just do:
declare
i integer := &a;
begin
null;
end;
/
As you have it you're doing an unnecessary implicit string-to-number conversion.
If you haven't explicitly turned them off, then you probably have a site or user profile that is doing the set define off, among other configuration settings. it's probably doing that for a reason, but if you currently only have a site profile then you could create your own user profile to override that. Just be aware of the effect of anything you change; you may have other scripts that rely on it being off, e.g. if you have data that has ampersands and it's been disabled to prevent issues interpreting those.