Create an interface class with a pure virtual function. Create another class that inherits from it, and give a concrete implementation of the pure virtual function.

HelloWorldInterface.cpp

// https://repl.it/LEHR

#include <iostream>
using namespace std;

class HelloWorldInterfaceA
{
  public:
    virtual void printHelloWorldA() = 0;
};

class HelloWorldInterfaceB : public virtual HelloWorldInterfaceA
{
  public:
    virtual void printHelloWorldB() = 0;
};

class HelloWorldObjectA : public virtual HelloWorldInterfaceA
{
  public:
    virtual void printHelloWorldA()
    {
      cout << "Hello World from A\n";
    }
};

class HelloWorldObjectB : public HelloWorldObjectA, public virtual HelloWorldInterfaceB
{
  public:
    virtual void printHelloWorldB()
    {
      cout << "Hello World from B\n";
    }
};

int main()
{
  HelloWorldObjectB helloWorldObjectB;
  
  for (int i = 0; i < 2; i++) {
    helloWorldObjectB.printHelloWorldB();
  }
  
  for (int j = 0; j < 3; j++) {
    helloWorldObjectB.printHelloWorldA();
  }
  
  return 0;
}