# Are there problems that a classical computer can solve and a quantum computer can never solve?

Apologies if this is a silly question. But I've heard quantum computers can solve problems that classical computers can't. What about the converse, are there any problems that a classical computer can solve and a quantum computer can never solve?

The classical computer only manipulates logic 0 and logic 1, composing the essence of the logical circuit. So the question that classical computers can solve is merely by manipulating logic 0 and logic 1, while quantum can easily mimic it by only manipulating $$|0\rangle$$ and $$|1\rangle$$. So I think there does not exist any question that classical computers can solve while the quantum computers cannot.
Consider a gate-based quantum computer. Such computer allows to implement so-called Toffoli's gate which under specific circumstances (in particular when input to target qubits is $$|1\rangle$$) behaves like logical gate NAND. Since NAND is a universal gate in classical computing, i.e. it allows to implement any Boolean function and thus any algorithm, also quantum computer is able to perform any classical algorithm.