method override and pointer to function

#include <iostream>
#include <cassert>
#include <stdexcept>

using namespace std;

// function override example
//
struct A
{
    int foo() { return 1; }
    // virtual function method is overriden with the override declaration in the next structure.
    virtual int bar() { return 1; }
    virtual int divy(int a, int b) { return a/b; }
};

struct B : A
{
    int foo() { return 2; }
    // override declaration makes it the master
    int bar() override { return 2; }
    int divy(int a, int b) override { return b/(2*a); }
};

// pointer to function example
//
int arithmetic(int, int, int (*)(int, int));
    // Take 3 arguments, 2 int's and a function pointer
    //   int (*)(int, int), which takes two int's and return an int
int add(int, int);
int sub(int, int);

int add(int n1, int n2) { return n1 + n2; }
int sub(int n1, int n2) { return n1 - n2; }

int arithmetic(int n1, int n2, int (*operation) (int, int)) {
   return (*operation)(n1, n2);
}

int main() {
    B b;
    A *a = &b;
    // it selects the A method hence value
    int v1 = a->foo();
    // override here selects the B method and hence its value
    //
    int v2 = a->bar();
    std::cout << " value v1 " << v1 << " value v2 " << v2 << std::endl;
    // add
    std::cout << arithmetic(v1, v2, add) << std::endl;
    // subtract
    std::cout << arithmetic(v1, v2, sub) << std::endl;
    assert(v1 == 1);
    assert(v2 == 2);

    A a2;
    a = &a2;
    // now its like type A only as it we set it to the address of A2
    v1 = a->foo();
    v2 = a->bar();
    std::cout << " value v1 " << v1 << " value v2 " << v2 << std::endl;
    assert(v1 == 1);
    assert(v2 == 1);

    // add
    std::cout << arithmetic(v1, v2, add) << std::endl;
    // subtract
    std::cout << arithmetic(v1, v2, sub) << std::endl;

    a = &b;

    // now we have addressed B but the return variable is a const declaration
    try {
      int v3 = a->divy(v2,0);
      std::cout << "v3 " << v3 << std::endl;
    } catch (const std::exception& e) { std::cout << e.what() << std::endl; }
    try {
       throw 20;                       // before we divide bv 0 throw it
       int v4 = a->divy(0,v2);
       std::cout << "v4 " << v4 << std::endl;
    }
    catch (int e)
    {
       cout << "divide by zero found first. " << e << '\n';
    }
    catch (const std::exception& e) { std::cout << e.what() << std::endl; }


    a = &a2;
    try {
      int v3 = a->divy(0,v2);
      std::cout << "v3 " << v3 << std::endl;
    } catch (const std::exception& e) { std::cout << e.what() << std::endl; }
    try {
      int v4 = a->divy(v2,0);
      throw std::runtime_error("Div zero stopped");
      std::cout << "v4 " << v4 << std::endl;
    } catch (const std::exception& e) { std::cout << e.what() << std::endl; }

    std::cout << " ended " << std::endl;
    return 0;
}