fgets() reads in at most one less than size characters from stream and stores them into the buffer pointed to by s. Reading stops after an EOF or a newline. If a newline is read, it is stored into the buffer. A \0 is stored after the last character in the buffer.
ungetc() pushes c back to stream, cast to "unsigned char", where it is available for subsequent read operations. Pushed - back characters will be returned in reverse order; only one pushback is guaranteed.
Calls to the functions described here can be mixed with each other and with calls to other input functions from the stdio library for the same input stream.
For non-locking counterparts, see unlocked_stdio(3).