If you do not specify a size for a CHAR column, the default is 1. You can see what I mean in the example below, which I tested on Oracle 11.2:
SQL> create table t1
2 (c1 char,
3 c2 char(1))
4 /
Table created.
SQL> desc t1
Name Null? Type
-------------------------- -------- ------------------
C1 CHAR(1)
C2 CHAR(1)
SQL>
However, if you rely on defaults like this and the software supplier changes them, you could be left with an application which does not work.