friend unary.cpp

#include<iostream>
using namespace std;

class demo
{
private:
    int x,y;
public:
    demo()
    {
        x=0;
        y=0;
    }
    demo(int a,int b)
    {
        x=a;
        y=b;
    }
    void show()
    {
        cout<<x<<" "<<y<<endl;
    }
    friend void operator-(demo &ob);
//    {
//        x=-x;
//        y=-y;
//    }
};

void operator-(demo &ob)
{
    ob.x=-ob.x;
    ob.y=-ob.y;
}

int main()
{
    demo obj(-10,20);
    obj.show();
    -obj;
    obj.show();

}