As with most linux these days, MINT is no longer setup for every
install being used by a programmer. So it no longer comes with the
traditional stuff like stdio.h. If you google linux mint stdio.h not
found
many people have run into the same problem and there is much
discussion if you are interested.
The short answer is to install build-essential
this is a package that brings your linux back to the traditional
programmer state with all the usual things like the includes and
libraries you are missing.
As to how to install build-essential, do:
sudo apt-get install build-essential
Again google has many walkthroughs for installing it on MINT, even
youtube videos.