Overloading Unary operator

In the following program the unary minus operator is used. A minus operator used as a unary, takes just one operand.

/* Program that Shows how the unary minus operator is overloaded. */

#include<iostream>

using namespace std;

class simple

{

    int x;

    int y;

    int z;

  public:

     void getdata(int a, int b, int c);

     void display(void);

     void operator-();   //overload unary minus

};

void space::getdata(int a, int b, int c)

{

    x=a; 

    y=b;

    z=c;

}

void space::display(void)

{

    cout<<"x="<<x<<" ";

    cout<<"y="<<y<<" ";

    cout<<"z="<<z<<" ";

}

void space::operator-()

{

    x=-x;

    y=-y;

    z=-z;

}

int main(){

    space S;

    S.getdata(120,-230,340);

    cout<<"S: ";

    S.display();

    -S;               //activates operator-() function

    cout<<"-S: ";

    S.display();

    return 0;

}

the output of the above given program would be:

S: x=120 y=-230 z=340

-S: x=-120 y-230 z=-340

Remember, a statement like 

S2=-S1;

will not work because the function operator-() does not return any value. it can work if the function is modified to return an object.

it is possible to overload a unary minus operator using a friend function as follows:

 friend void operator-(space &s);     //declaration

 void operator-(space &s)                //definition

{

    s.x = -s.x;

    s.y = -s.y;

    s.z = -s.z;

}