I have 3 question about C++(continue)

Question

class Animal{
public:
virtual void bark()=0;// I confused at here. Why we assign to function a 0?
};
class Dog:Animal{
public void bark(){
cout<<"Woof";
}
};

Answer 1

I never thought of why tbh.

https://stackoverflow.com/questions/2156634/why-is-a-pure-virtual-function-initialized-by-0

Answer 2

tbh - "To be honest"

Answer 3

Thank you for answer. I am wondering what is the meaning of tbh? My English is not well.