It is a widely used computer language; one of the reasons is that it is a stricter way of compiling C code if you just use the procedural aspect of the language. Along with that, it has the object oriented model as well. Some would call it a 'better C' language.
Is an important thing to do.
Yes, because C++ is a very popular language, and many systems are written in C, C++, or Java. (C is the predecessor of C++, and Java is similar to C++ in many ways.)
The most important capability is Object Oriented Programming (OOP) principals, which necessitated the inclusion of classes. That was the main reason Bjarne Stroustrup developed C++ in the first place (indeed, C++ was originally called 'C with Classes').
b+b+b+c+c+c+c =3b+4c
c + c + 2c + c + c = 6c
b + b + b + c + c + c + c = 3b + 4c
4c
c + c + c + c + c = 5 * c.
There are no "primary and secondary keys" in c and c plus plus.
3c
There is no such thing as 'unix C++'.
They do exist in C and C++.