Operations through global friend functions

#include <iostream>
class Complex {
  int m_real;
  int m_imag;

public:
  Complex() {}

  Complex(int real, int imag) : m_real(real), m_imag(imag) {}

  void display() {
    // print m_real, m_imag in a+ib format
  }
  friend Complex add(const Complex &r1, const Complex &r2);
  friend Complex multiply(const Complex &r1, const Complex &r2);
  friend Complex subtract(const Complex &r1, const Complex &r2);
  friend bool equals(const Complex &r1, const Complex &r2);
};
Complex add(const Complex &r1, const Complex &r2) { // c1.add(c2)
  int treal = r1.m_real + r2.m_real;                // this->m_real + ref.m_real
  int timag = r1.m_imag + r2.m_imag;
  //Complex temp(treal, timag);
  //return temp;
  return Complex(treal,timag);
}

Complex multiply(const Complex &r1, const Complex &r2) {
  // TODO
}

Complex subtract(const Complex &r1, const Complex &r2) {
  // TODO
}

bool equals(const Complex &r1, const Complex &r2) { // c1.equals(c2)
  return r1.m_real == r2.m_real && r1.m_imag == r2.m_imag;
}

int main() {
  Complex c1(2, 3);
  Complex c2(4, 5);
  Complex c3, c4, c5;

  c3 = add(c1, c2);
 
  c5 = multiply(c1, c2);

  if (equals(c1, c2))
    std::cout << "yes";
  else
    std::cout << "no";

  return 0;
}