Is there anything that can be programmed on a classical computer but not on a quantum computer?

Question

Would we need to create new algorithms that only work on quantum computers or would be simply edit codes in languages such as C++ to involve the new primitives from quantum computing? Are there things that can be programmed on a classical computer that can’t be programmed ona. Quantum computer? I know that quantum computer are turing complete.

Answer 1

Short answer: no. Any classical algorithm can be transformed into quantum algorithm. This result has little practical value, because you don't obtain quantum speedup, but it is important from theoretical point of view.