Challenge 1: Vector2D With operator+ — Possible Solution
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#include <iostream>

class Vector2D {
public:
    double x, y;

    Vector2D operator+(const Vector2D &other) {
        return Vector2D{x + other.x, y + other.y};
    }
};

int main() {
    Vector2D v1{1, 2};
    Vector2D v2{3, 4};
    Vector2D sum = v1 + v2;

    std::cout << sum.x << ", " << sum.y << std::endl;

    return 0;
}

Output:

    4, 6

WHY THIS WORKS AS AN ANSWER
------------------------------
v1 + v2 reads naturally as ordinary addition syntax, but under the
hood it calls v1.operator+(v2) -- v1 supplies the implicit this (the
left operand), v2 is the explicit other parameter (the right operand)
-- producing a new Vector2D whose x and y are each operand's respective
components summed, exactly matching the chapter's own pattern.