Why we are using iostream at here, where as in turbo c++ compiler, we use it as iostream. h?

Because it is simply 2017, and Turbo C++ was last updated in 1996. C++ has come a long way from that compiler... This question translates to : Why use Windows 10 when we have Windows NT?

Here's the true reason... members.gamedev.net/sicrane/articles/iostream.html