How to do non-blocking keyboard input

[Russell Taylor]

	I want to do non-blocking keyboard I/O in a program.  Basically, the
routine will read a character from the keyboard if there is one and return
NULL if there is not.  This is done in a tight loop with reads and writes
to other devices.  How to I get a character from the keyboard if there is
one and a NULL if there is not?

	Thanks,
	Russell Taylor
	taylorr at cs.unc.edu