Why the error?

struct Statistics \{ // default constructs swaps and compares to zero std::size_t numSwaps {0}; std::size_t numCompares {0}; In file included from driver.cpp:65: ./sort.hpp:26:15: error: function definition does not declare parameters std::size_t numSwaps {0}; ./sort.hpp:27:15: error: function definition does not declare parameters std::size_t numCompares {0}