example3_operator_overloading_friend_functinons.cpp

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#include <iostream>

class Complex {
private:
    double real;
    double imag;

public:
    Complex(double r = 0.0, double i = 0.0) : real(r), imag(i) {}

    Complex operator+(const Complex& other) const {
        return Complex(real + other.real, imag + other.imag);
    }

    friend std::ostream& operator<<(std::ostream& os, const Complex& c);
    friend Complex operator*(const Complex& a, const Complex& b);
};

std::ostream& operator<<(std::ostream& os, const Complex& c) {
    os << c.real;
    if (c.imag >= 0) os << "+";
    os << c.imag << "i";
    return os;
}

Complex operator*(const Complex& a, const Complex& b) {
    return Complex(a.real * b.real - a.imag * b.imag,
                   a.real * b.imag + a.imag * b.real);
}

int main() {
    Complex a(1, 2);
    Complex b(3, 4);

    std::cout << "a = " << a << std::endl;
    std::cout << "b = " << b << std::endl;
    std::cout << "a + b = " << a + b << std::endl;
    std::cout << "a * b = " << a * b << std::endl;

    return 0;
}