What C++ IDEs are available for iPhone?
There are no native IDE available for iOS. Apple restricts unsigned code from being run on all iOS devices, thus making an IDE on iOS impossible. (this is possible on android to run code directly on the device that is written on device)

Your best bet is to get a regular text editor such as nimbus or anything that can checkout documents and edit them from git, svn or dropbox. You will never be able to run this code on iOS, so you will need to push it to your repository and compile and run it via a remote desktop client or via a SSH terminal. 

To really fully automate this process you would have to edit your code, push it to the repository, compile it on another machine and then have that compiled binary shipped to your device using a distribution mechanism like testflightapp via a series of scripts (test flight has an API for this). It's not impossible, just hard. 

Another option is to use a remote desktop client and remote to an IDE on a PC to edit and run your code there.