C++ quiz. What will the following program print? <pre><code

What will the following program print?

#include <iostream>

struct A;

int operator+(const A&, const A&) {
    return 3;
}

struct A {
    operator int() {
        return 1;
    }
};

int main() {
    A a, b;
    std::cout << a + b;
}

```
1
```
```
2
```
```
3
```
Runtime error
Compilation error

Explanation

13.3.1.2 Operators in expressions
...
The set of candidate functions for overload resolution is the union of the member candidates, the non-member candidates, and the built-in candidates. The argument list contains all of the operands of the operator. The best function from the set of candidate functions is selected according to 13.3.2 and 13.3.3.119)