Hey, I am currently wasting my life away over the summer, so I was wondering what's some great activities i can do with a bunch of free time that can strengthen my C++ knowledge while helping me tackle interview questions.

You can try to solve some problems on http://www.spoj.com/ or any other similar online judge (https://en.wikipedia.org/wiki/Online_judge ).

These should provide enough study material.
https://www.google.co.uk/search?q=interview+questions+c%2B%2B&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&ei=AxWDWeDmKejGXuvrjvgP