After closing a file, the file and its file number are no longer associated and subsequent I/O operations using this file number will be invalid until the file number is specified in another open statement. Once a file is closed, its file number is free to be used for a subsequent open of the same file or any other file. Similarly, the file just closed may be reopened with the same file number or any other unused file number.
When a file previously opened for sequential output is closed, the output buffer is automatically flushed prior to the close.
v = 1 close v, #2, #v+2cause the files associated with file numbers 1, 2, and 3 to be closed.
closecauses all open files to be closed.
from The Basmark QuickBASIC Programmerís Manual by Lawrence Leinweber