C++ How works set of function's argument value?

Question

I am learning C++ and I have code:

float x, y;

namespace X {
    void SetMyX(float p) {
        x = p;
    }
    void SetMyY(float p) {
        y = p;
    }
    namespace XY {
        void Set(float p = 0.0f) {
            x = p;
            p = y;
        }
    }
}

int main() {
    X::SetMyX(5.4f);
    std::cout << "x = " << x << " y = " << y << std::endl;
    X::SetMyY(4.1f);
    std::cout << "x = " << x << " y = " << y << std::endl;
    X::XY::Set();
    std::cout << "x = " << x << " y = " << y << std::endl;
    return 0;
}

And output is:

x = 5.4 y = 0
x = 5.4 y = 4.1
x = 0 y = 4.1

And I figure out variable p sets value of x and then y sets value of p ? But, how it is possible? In C++ you can also set value of function's argument or what? It's just weird for me because I thought you can't just "editing" entered value and you must add another variable like result or something like that, or just return sum of two arguments, but change them?

Answer 1

Yes, the argument p is a completely normal variable and you can do everything with it.

This will also work in many other languages like C, Java, Javascript or Python.