Hello,
Out of fgets() and gets() which function is safe to use and why?

Thanks

It depends where you are using :
fgets reads characters from stream into the string s. It stops when it reads either n - 1 characters or a newline character, whichever comes first.
gets collects a string of characters terminated by a new line from the
standard input stream stdin and puts it into s.

Also fgets() takes 'number of bytes to be copied' as an argument, which is a very good practice as it never lets you in problems like 'buffer overflows'...Use of gets() is generally discouraged..
For further info: man fgets (if you are on linux)

gets() is NEVER safe to use because it can corrupt the memory of your program and cause it to crash (or coredump in *nix). Read this explaination.