Pure c++ app for Android and its performance

Yes and yes, althrough Google says:

"Using native code does not result in an automatic performance increase, but always increases application complexity... If you write native code, your applications are still packaged into an .apk file and they still run inside of a virtual machine on the device. The fundamental Android application model does not change."

from http://developer.android.com/sdk/ndk/index.html

(Personally, I don't agree that writing in C++ automatically makes a more complex program than Java, I'd even say it's the other way around for a skilled C++ programmer)