I'm having trouble understanding this challenge question (C++)

Question

So here's the question:

What's the output?

#include <iostream>
using namespace std;

class A
{
public:
virtual void f() { cout << 1; }
};

class B: public A
{
private:
void f() { cout << 2; }
};

void c(A &a) { a.f(); }

int main()
{
B b;

c(b);

return 0;
}

The output is 2. However, I noticed that if you remove the '&' from the c function, it returns 1 instead.

I've been trying to search online about how passing parameters like this works, but the example always use pointers (ie: something like A* a or int* x instead).

HOWEVER, when you try to use a pointer here, it tells me that the argument cannot be converted from class 'B' to 'A'. Which, to me, makes sense. I still just don't understand why using &a works here.

Thank you in advance if you're able to help me understand this :D

Answer 1

Thank you, Gordie. You're awesome, and I just learned a lot from that lesson. I guess I should really go through that website if I really want to understand C++.

Answer 2

@Gordie Could you possibly point out my error? I simply changed '&a' to '*a' and it's still the error I get. (Also tried A* a just in case).

Also, still reading through the link.

https://code.sololearn.com/cHlhkxCo3q1a/?ref=app