which headers should i add to my new class?

[ardavan]

how can i find that which headers should I add to my new class?

[Repeater]

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?