Could someone test if it also works on 32-bit Systems
I'm currently running a 64-bit Windows version so I can't tell you this for certain, but I'm pretty confident that if users install a 32-bit version of 7Zip on their machine (which will be stored under "C:\Program Files (x86)\") your program won't pick it up. Make sure you do a programmed scan for 7Zip in both "Program Files" and "Program Files (x86)" if they're on a 64-bit machine.
I notice you're currently using the system() method a lot in order to avoid writing C++ code. That's fine if you're just starting out, but if you really want to learn from what you're writing you should focus on doing things manually (or through pure C++ code) instead of relying on passing batch code through to get things done.
One other thing while I'm making suggestions: make sure you style your code. It's better to start drilling this into your head now rather than later before you start picking up bad habits. Your un-styled code is another coder's worst nightmare because reading unfamiliar code that's all over the place just screws with you. A quick Google search yielded the following page that gives some pointers on how to style your C++ code properly (
http://geosoft.no/development/cppstyle.html).
Finally, kudos to you. C++ isn't the starting language of choice for many people due to the popular belief that it's towards the end of the spectrum as far as difficulty goes. You've done a good job