how can i find that which headers should I add to my new class?
If you use a class or function from some header, then you need to include that header.
If you use something from the header <string> , then you need to #include <string>
If you use something from the header <algorithm> , then you need to #include <algorithm>
You need to add the headers for what you're making use of. What are you making use of that comes from header files?