The iostream.h library has been depreceted, and replaced with iostream. Functionally they are generally the same, but iostream is now part of the 'std' namespace.
Either g++ no longer supports the deprected iostream.h, or you may be using the two interchangably.
using namespace std; // Without this you would have to use std.cin or std.cout
cout << "Enter num: ";
cin >> input;
cout << "\nYou input: " << input;