Nạp chồng toán tử gọi hàm () trong C++

#include <iostream>
using namespace std;

class KhoangCach
{
private:
    int met;
    int centimet;
public:
    // phan khai bao cac constructor can thiet
    KhoangCach() {
        met = 0;
        centimet = 0;
    }
    KhoangCach(int m, int c) {
        met = m;
        centimet = c;
    }
    // nap chong toan tu goi ham ()
    KhoangCach operator()(int x, int y, int z)
    {
        KhoangCach K;
        // bay gio, dat phep tinh bat ky
        K.met = x + y + 5;
        K.centimet = y - z + 20;
        return K;
    }
    // Phuong thuc de hien thi khoang cach
    void hienthiKC()
    {
        cout << "\nDo dai bang m la: " << met << 
            "\nVa do dai bang cm la: " << centimet << endl;
    }

};

int main()
{
    KhoangCach K1(25, 40), K2;
    cout << "Khoang cach dau tien la: ";
    K1.hienthiKC();   K2 = K1(15, 15, 15);
    // trieu hoi toan tu ()
    cout << "\n--------------------------\n";
    cout << "Khoang cach thu hai la: ";
    K2.hienthiKC();   return 0;
}