> I never really got the whole public/private thing.
It's about encapsulation and class invariants. Public methods must preserve them, private methods can break them temporarily. You get a prepackaged component and you're prevented from introducing bugs into the component from the outside of the component.
Take std::vector, for example. By keeping implementation details (pointer to element storage and element count) private, you prevent users of the class to accidentally shoot themselves in the foot by, say, changing the element count directly.
You could use interfaces, but for that you have to use virtual functions: Objects have to be created dynamically and you have to handle pointers or references instead of values.
It's about encapsulation and class invariants. Public methods must preserve them, private methods can break them temporarily. You get a prepackaged component and you're prevented from introducing bugs into the component from the outside of the component.
Take std::vector, for example. By keeping implementation details (pointer to element storage and element count) private, you prevent users of the class to accidentally shoot themselves in the foot by, say, changing the element count directly.
You could use interfaces, but for that you have to use virtual functions: Objects have to be created dynamically and you have to handle pointers or references instead of values.