Overloading as Friend functions

Operators can be overloaded as global/friend functions also, besides member functions approach
In such case, no. of arguments vary as follows, as global/friend functions are not members of the class

• For the binary operator, the function takes two arguments, where the first argument represents operand1 and the second argument represent operand2
• For a unary operator, function takes one argument, which is the sole operand.
• For post-increment, the function takes two arguments, the first argument is the operand, and the second argument is the dummy integer.

Here is an equivalent syntax for friend functions, when the following expressions are requested.
 

t1+t2     ==> operator+(t1,t2)
t1+10     ==> operator+(t1,10)
++t1      ==> operator++(t1)
t1++      ==> operator++(t1,int)
t1==t2    ==> operator==(t1,t2)
t1=t2     ==> not possible as non member function

Let’s add following friend declarations to MyTime class with suitable definitions.

friend MyTime operator+(const MyTime& r1,const MyTime& r2);
friend MyTime operator+(const MyTime& r1,int);
friend MyTime& operator++(MyTime& ref);
friend MyTime operator++(MyTime& ref,int);
friend bool operator==(const MyTime& r1,const MyTime& r2);


Complete Code

class MyTime {
  int hh;
  int mm;

public:
  MyTime():hh(0),mm(0) { }
  MyTime(int hh, int mm) : hh(hh), mm(mm) {}
  MyTime(const MyTime &ref) : hh(ref.hh), mm(ref.mm) {}

  friend MyTime operator+(const MyTime &r1, const MyTime &r2);
  friend MyTime operator+(const MyTime &r1, int);
  friend MyTime& operator++(MyTime &r1);
  friend MyTime operator++(MyTime &r1,int);
  friend bool operator==(const MyTime &r1, const MyTime &r2);
  friend bool operator<(const MyTime &r1, const MyTime &r2);
};
MyTime operator+(const MyTime &r1, const MyTime &r2) { // t1 + t2
  int th = r1.hh + r2.hh;
  int tm = r1.mm + r2.mm;
  return MyTime(th,tm);
}
MyTime operator+(const MyTime &r1, int nm) { // t1 + 5
  int th = r1.hh;
  int tm = r1.mm + nm;
  return MyTime(th,tm);
}
MyTime& operator++(MyTime &r1) { // ++t1
  ++r1.mm;
  return r1;
}
MyTime operator++(MyTime &r1,int dummy) { //t1++ 
  MyTime orig(r1);
  ++r1.mm;
  return orig;
}
bool operator==(const MyTime &r1, const MyTime &r2) { // t1 == t2
  return r1.hh == r2.hh && r1.mm == r2.mm;
}
bool operator<(const MyTime &r1, const MyTime &r2) { // t1 == t2
  //TODO
}
int main() {
  MyTime t1(10, 20);
  MyTime t2(1, 15);
  MyTime t3, t4, t5, t6;
  t3 = t1 + t2; // operator+(t1, t2)
  t4 = t1 + 50; // operator+(t1, 50)
  t5 = ++t1;    // operator++(t1)
  t6 = t1++;    // operator++(t1,int)
  if (t5 == t6) // operator==(t5, t6)
    std::cout << "Equal\n";
  else
    std::cout << "Not Equal\n"; 
}