let's get something straight, essentially C++ is C. Most of what can be done in C++ can also be done very easily in C. Many of the oop aspects of C++ can easily be done in C. The difference however is, C++ was built around these concepts, therefore it provides clearer and easier ways of implementing object orientated methologies. C++ is also considered to be 'bloatware' because it provides many new ways of performing various methods through the use of methods within class objects. However, the older counter parts for things like io can still use the C library. As a matter of fact, every C function is available to C++ as long as you include its library. However, since C++ is a standardized language, it is generally more accepted to use C++'s libraries (although you will find yourself needing C's sooner or later). C++ can be a little daunting for a beginner to programming because of all the methologies the standards require it to encompass but the latter will prove much more rewarding that simply learning C. For the time being, it is essential in programming to be able to understand and implement oop methologies as companies and many projects are created in a modularized way. Meaning, if your program should comprise 3 tasks, those 3 tasks should be writen as 3 seperate programs independant of each other that may be able to work with other tasks or perhaps alone through encapsulation. C++ provides that boundaries to do this simply enough. As long as you can work in C++, it is fairly safe to say that you can code in C because then it is only a matter of learning libraries not languages.

As for linux distros writen in C++, such a thing cannot exist. The linux kernel was writen in C, this is the foundation of the OS. As for applications available for it, i am sure many are infact writen in C++ but the operating system itself is not.