In parser programs it is often useful to examine the next character in the input stream without removing it from the stream. This is called ``peeking ahead'' at the input because your program gets a glimpse of the input it will read next.
Using stream I/O, you can peek ahead at input by first reading it and then unreading it (also called pushing it back on the stream). Unreading a character makes it available to be input again from the stream, by the next call to fgetc or other input function on that stream.
| Unreading Idea | An explanation of unreading with pictures. |
| How Unread | How to call ungetc to do unreading. |