What is the difference between a friend function for a class and a member function for the class?

A friend function is a function that is not a member of a class but has access to the class's private and protected members. Friend functions are used to extend the functionality of a class without modifying the class itself. A member function, on the other hand, is a function that is declared within a class and is part of that class. It has access to the members of the class and can interact with them. Member functions are used to define the behavior of a class.

Friend functions have access to private and protected members of the class because they are declared as friends of the class. This allows them to operate on the class's data members directly. However, they do not have access to the class's methods as those are part of the class itself. Member functions have access to all the members (data and functions) of the class, private and protected included, as they are part of the class itself.

Friend functions are declared using the keyword 'friend' followed by the function declaration inside the class definition. ```cpp class ExampleClass { private: int data; public: friend void friendFunction(ExampleClass&); }; ``` Member functions are declared within the class definition without the 'friend' keyword: ```cpp class ExampleClass { private: int data; public: void memberFunction(); }; ```

Friend functions are called like regular (non-member) functions, using the object of the class as an argument: ```cpp ExampleClass obj; friendFunction(obj); ``` Member functions are called using the object of the class and the dot (.) operator: ```cpp ExampleClass obj; obj.memberFunction(); ``` In summary, a friend function is not a member of a class but can access its private and protected members, while a member function is a part of the class and can access all its members. Friend functions are declared using the 'friend' keyword, and member functions are declared within the class without this keyword. Friend functions are called like regular functions with the object as a parameter, while member functions use the dot operator.