To learn C ++ is it necessary to learn C?

No. In some ways it is even recommended that you do not learn C. You can even, but this can confuse you. If you have decided to go to C ++, go there. Most excellent C ++ programmers will admit they do not know C.

There is a myth that C ++ is the "improved" C, but this is not true. C ++ started being an evolution of C, but so many new features were put that turned another language. Although C ++ compiles almost all C-codes, this is not the way to program in C ++. If you program in C ++ for real the code is very different from the C code.

And then you have to be careful with the material you will choose to learn because many teach C in C ++, that is, you do not even know you are cheating, because it works, but it is not right,

C ++ is a high-level language with best cost zero abstractions and is evolving a lot. C is considered a portable Assembly, and even so it hardly evolves and has almost no abstractions.

My consumer dream is that C ++ has a way that turns off the ability to use C resources.