getch() is provided from conio.h so therefor you have to include conio.h in your header like this.
ALthough I want to point out that getch is a non portable C function and everything else in your code looks to be C++. It is a better practice to pick one languish and then stick to that. Replace getch with cin.getline(); or some other appropriate C++ method and your code will be more concistant.
using namespace std;
//the rest of your program