int ungetc(int __c, FILE *__stream)
The ungetc() function pushes the character
c (converted to an unsigned char) back onto the input
stream pointed to by stream. The pushed-back character
will be returned by a subsequent read on the stream.
Currently, only a single character can be pushed back onto the stream.
The ungetc() function returns the character pushed back after the
conversion, or EOF if the operation fails. If the value
of the argument c character equals
EOF, the operation will fail and the stream will
remain unchanged.