DOS C complier.

Originally Posted by Adak

io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.

Originally Posted by Salem

You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

Outside of your DOS world, your header file is meaningless.

For information on how to enable C++11 on your compiler, look here.
よく聞くがいい！私は天才だからね！ ^_^