Overloading ++ and -

• Increment/decrement operators can be overloaded
  • Add 1 to a Date object, d1
  • Prototype (member function)
    • Date &operator++();
    • ++d1 same as d1.operator++()
  • Prototype (non-member)
    • Friend Date &operator++( Date &);
    • ++d1 same as operator++( d1 )
• To distinguish pre/post increment
  • Post increment has a dummy parameter; int of 0
  • Prototype (member function)
    • Date operator++( int );
    • d1++ same as d1.operator++( 0 )
  • Prototype (non-member)
    • friend Date operator++( Data &, int );
    • d1++ same as operator++( d1, 0 )
  • Integer parameter does not have a name; not even in function definition
• Return values
  • Preincrement
    • Returns by reference (Date &)
    • lvalue (can be assigned)
  • Postincrement
    • Returns by value
    • Returns temporary object with old value
    • rvalue (cannot be on left side of assignment)
• Decrement operator analogous