Is it safe to do a TO_NUMBER(TO_CHAR(:n)) ?

var n number
exec :n :=  9.9999999999999999999999999999999999e125
select to_number(to_char(:n)) from dual;
ORA-01722: invalid number

SQL Reference
If a positive NUMBER value is extremely large and cannot be represented in the specified format, then the infinity sign (~) replaces the value

select to_char(:n) from dual;

I wrote more about infinity here

committing transaction

When and how do you commit a transaction?

SQL> insert into lsc_t(x) values(1);         ... (1) not committed
SQL> commit;                                 ... (1) committed

SQL> insert into lsc_t(x) values(2);         ... (2) not committed
SQL> alter table lsc_t disable primary key;  ... (2) committed

SQL> set autocommit ON
SQL> insert into lsc_t(x) values(3);         ... (3) committed
SQL> set autocommit OFF

SQL> insert into lsc_t(x) values(4);         ... (4) not committed
SQL> disc                                    ... (4) committed

Row 1 is committed after the commit keyword.

Row 2 is implicitely committed after before the alter table ddl statement.

Row 3 is autocommitted. Autocommit exists in sqlplus, but is more often seen in stateless applications (for instance a web application).

Row 4 is committed after a successfull disconnection.

But what appends if you kill your current session?

SQL> insert into lsc_t(x) values (5);

1 row created.

SQL> !ps
 13903 pts/33   0:00 ksh
 22384 pts/33   0:00 sqlplus

SQL> !kill 22384

The row 5 is not commited

Ref: Overview of Transaction Management

A transaction ends when any of the following occurs:
– A user issues a COMMIT or ROLLBACK statement without a SAVEPOINT clause.
– A user runs a DDL statement such as CREATE, DROP, RENAME, or ALTER (*).
If the current transaction contains any DML statements, Oracle Database
first commits the transaction, and then runs and commits the DDL statement
as a new, single statement transaction.
– A user disconnects from Oracle Database. The current transaction is committed.
– A user process terminates abnormally. The current transaction is rolled back.

(*) but not ALTER SESSION

Please read On Implicit Commit