On some platforms (unix, for example) devices are handled as special files.
C: there are no methods in C. C++: no.
c is procedure oriented and c++ is object oriented & much newer.
If a + b + c + d + 80 + 90 = 100, then a + b + c + d = -70.
C++ is related to C, the language from which it is derived.
println is not a C++ keyword.
Cpp(C++) is used to make 'Many' programs because it is universal across many devices.
I believe that's usually treated as an axiom, meaning you don't prove it.
You use output devices or streams, typically console screens, printers and files.
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++.