Overloading the Short-Hand Operators (+= and -=)

The short-hand addition (+=) and subtraction (-=) operators are very commonly
used and thus it would be nice if we overload them in classes. You would be
glad to know that there is nothing new or special that needs to be done to achieve
this, both the operators are overloaded as usual like other binary operators.

The short-hand operators combine the operation performed by two operators one
the addition or subtraction and the other the assignment. This is all it does
and this is all you need to know!

As nothing new has been introduced so we end the theory here and look at the
example:


  // Program to illustrate the
  // overloading of shorthand
  // operators (+=, -=)
  #include <iostream.h>

  class myclass
  {
    int a;
    int b;

  public:
    myclass(int,int);
    void show();

    myclass operator+=(myclass);
    myclass operator-=(myclass);
  };

  myclass::myclass(int x,int y)
  {
    a=x;
    b=y;
  };

  void myclass::show()
  {
    cout<<a<<endl<<b<<endl;
  }

  myclass myclass::operator+=(myclass ob)
  {
    a+=ob.a;
    b+=ob.b;

    // note this
    return *this;
  }

  myclass myclass::operator-=(myclass ob)
  {
    a-=ob.a;
    b-=ob.b;

    // note this
    return *this;
  }

  void main()
  {
    myclass ob1(10,20);
    myclass ob2(100,200);

    ob1+=ob2;

    ob1.show();

    // even this is possible
    // because operator functions
    // are retuning *this
    ob2=ob1+=ob1;

    ob2.show();
  }