Can somebody please explain this step-by-step?

Question

#include <iostream>

int f(int &a, int &b) {
a = 3;
b = 4;
return a + b;
}

int main() {
int a = 1;
int b = 2;
int c = f(a, a);
std::cout << a << b << c;
}

Why output is 428?

Answer 1

When both arguments are a, you need to remember that the same variable is controlled, and one variable can only hold one value.

The function would literally assign 3 to a, and then override the previous assignment with 4 to a, and then return 4+4.
Hence the output is 428

Answer 2

I got it, thanks!