I see you're from India (which part, BTW?), so before I suggest *anything* I'd like to tell you this : if you're using Turbo C++, you're shooting yourlsef in the foot. Turbo C++ is an old, non standard, 16 bit DOS IDE that went out of fashion in 1995. It's a shame Indian universities still use it. I don't know what compiler you're using, but I included this bit of information for the sake of completeness. If you're using GCC, just ignore this paragraph.
For cross platform development, get the GNU Compiler Collection (or GCC). In Ubuntu :
To compile C++ :
sudo apt-get install build-essential
My exams also end tomorrow, and I'm learning Qt for cross platform development. It's the toolkit of choice for KDE development and is also heavily used by Skype, Google Earth and VLC, to name a few. Probably the best choice for cross platform GUI development using C++. Why don't you take a look?
g++ <FILENAME>.cpp -o <OUTPUT_FILE_NAME>
I'm going to spend the next 15 days building small applications. A few ideas I have are :
1. A media player (made dead simple, thanks to Phonon)
2. Sticky notes (I recently switched to a Mac and I really miss Tomboy)
3. A simple text editor
4. An RSS reader
None of these are particularly difficult since Qt provides several libraries for networking, XML, databases etc.