c++基本语法---重载一元运算符

#include 
using namespace std;
class Distance{
	private:
		int feet;
		int inches;
	
	public:
		Distance(){
			feet = 0;
			inches = 0;
		}
		Distance(int f, int i){
			feet = f;
			inches = i;
		}
	
		void displayDistance(){
			cout << "from " << feet << " to " << inches << endl;
		}
	
		Distance operator-(){
			feet = -feet;
			inches = -inches;
			return Distance(feet, inches);
		}
};
int main()
{	
	Distance D1(11,10), D2(-5,11);
	
	-D1;
	D1.displayDistance();
	
	-D2;
	D2.displayDistance();
    return 0;
}