how to define addition for a class operator in cpp code example

Example 1: c++ operator overloading

// money.h -- define the prototype
class Money
{
   public:
      Money & operator += (const Money &rhs);
}

// money.cpp -- define the implementation
Money& Money :: operator += (const Money &rhs)
{
   // Yadda Yadda
  
   return *this;
}

Example 2: operator overloading in c++

Box operator+(const Box&);