Call of Duty, like more or less every modern AAA game, is indeed written in C++.

Call of Duty: Modern Warfare 2.

You'll find a lot of free games to pass the time in the App Store for your iPhone. Many of them have in-app purchases that can help you proceed quicker or give you a leg up, but if you want to keep your wallet closed, you can play them without spending a dime.

Downloading games onto your iPhone does not inherently harm the device. However, continuously downloading and deleting large games or having many apps running in the background can potentially impact the device's performance over time.