Files

RFO-BASIC! programs can use files that are in internal storage or on a removable device such as an SD card. (Android phones often have an SD card inside. It is an alternative "removable" storage space, though it may be difficult to actually remove it.)  With an adapter attached to the USB port, a removable device may also be a thumbdrive. By default, files reside in a directory called  in the same place (on the same device) where you installed RFO-BASIC!.

Files are sequences of bytes. Traditional (8-bit) characters can be stored as bytes. UNICODE characters can be stored as multiple bytes. However, some RFO-BASIC! programs transform these characters.

Files have names, which the program must specify to open the file in order to gain access to its contents.
 * Alphabetic case in filenames
 * Files stored on SD cards and thumbdrives use the Microsoft FAT file system, in which the case of letters is unimportant. A file named   can be used by specifying   or   or other combinations of uppercase and lowercase.
 * Files stored in the phone's internal storage use the Linux file system, in which the case of letters is important. Each of the variations given above would refer to a different file.

Programmers need to pay attention to this because it can lead to unusual errors. For example, if an RFO-BASIC! program capitalized all filenames to be helpful to the user, then a file with lowercase in its name, which was accessible on a removable drive, would suddenly become inaccessible if moved to the phone's internal storage. To prevent errors, RFO-BASIC! programs should always assume a filename could contain lowercase letters, and should match case exactly in file paths and names.