Porting Between Linux and Windows

[Eric Tavenner <estavenner gmail com>]

I am trying to teach myself C++.  My goal is to be able to write code for
the same app in either Linux or Windows, and compile for both from the same
code.  Is this possible?
I have Code::Blocks 10.05 on both OSes, (Fedora 17 and Windows 7) on a 64
bit machine.  Currently Fedora has GTK 2.24.10 and Windows has 2.22.1.  Is
this going to cause problems with compiling?

I have some experience with many versions of basic, but almost none with C
or C++, so please keep your answers simple.
Thanks.
Eric Tavenner