redirecting stdin from within a program - HELP!

[Amy Jo Bilson]

Does anyone know of a way to read a file from stdin (using redirection
or pipes) and then, when the input has been read (i.e. no more characters
on input), to get some info from the keyboard? I assume that there is some
mechanism to redirect the file descriptor for stdin from within a C 
program, but I haven't found it yet. If anyone knows how to do this, and
could send me a code fragment illustrating the procedure, I'd be much
obliged.

Thanks in advance.

Amy Jo Bilson
ARPA: ames!amyjo at riacs
UUCP: ames!amyjo