Calling a function from one class in another class

Question

If I have these two sets of .cpp and .h files set up like this and I l want to put an add() function in a.cpp that adds ten integers and returns sum. Then I have class b that will return the average but I want to use the sum of the ten integers that I got from class a . How can I call function add() in function average() so it can return the sum? I don't know if this is getting my question across well, I just made this example up to try it illustrate it.

class a { 
  private: 
    int a[10];  
  public: 
    a( ); 
    int add( int); 
}; 

class b {
  private:  
    int d; 
  public: 
    int average(int ); 
}  

Answer 1

You can call member functions on an object of a class, not on the class itself. Creating an object is almost as creating a variable, for example a my_a; . Then you can use the add member function of the my_a object as my_a.add(42) .

If you do not need objects (but do need classes for some reason), use static member functions and variables as follows.

class MyClass {
private:
  static int variable;
public:
  static int accessor() { return variable; }
};

In this case, you can call the static member function without creating an instance as MyClass::accessor() .

Answer 2

class A {
   public:
      static int add(int);
};

class B {
   public:
      void average(int val){ 
          A::add(val);
          // Some logic 
      }
};