Can a program be made such that the system declares a new variable?

Answer 1

Yes, with dynamic memory (new and delete) the program can handle memory as needed at run-time.

Answer 2

C++ is linked/compiled (not interpreted) which negates the question in the strictest sense. Mattias is correct from the dynamic sense.

If you still want to know how to do this as if the linker/compiler knew about the variable (you'll be certain you do, not just wondering - and you'll understand the security architectures that seek to block you) you might have better luck at StackExchange. Even if you have an excellent reason, be prepared for lots of pushback for people who won't agree this is necessary.

Answer 3

u meam?