D.

Postfix requires an int parameter. With no parameters you will be overloading prefix.

Also postfix should return by value and of course it has to be a class method and not a freestanding function.

Class Type
{
...
Type& operator++ () // prefix
{

Increment(*this); // whatever you want it to mean...

return *this; // return the resulting value by reference

};

Type operator++ (int) // dummy not used

{

Type temp *this;

++(*this); // implement postfix in terms of prefix

return temp; // return the original value by value

}
}