Understanding the use of ungetc()

hello friends...i need some help again.it's little hard to understand that whats the use of
ungetc() function.Can you people explain that with some examples.please..i'm still learning.And new to this stuff..

 

refer to this:-
http://www.cplusplus.com/reference/clibrary/cstdio/ungetc/
If you still dnt understand the tutorial then refer back to me.....