直接写参数列表里就好啦

#include <iostream>
using namespace std;

class Base {

  private:
    int x;
    int y;

  public:
    Base(int x, int y) {
        this->x = x;
        this->y = y;
    }

    int getX() {
        return x;
    }

    int getY() {
        return y;
    }

};

class Sub : public Base {

  private:
    int z;

  public:
    Sub(int x, int y, int z): Base(x, y), z(z) {}

    int getZ() {
        return z;
    }

    int calculate() {
        return Base::getX() * Base::getY() * this->getZ();
    }

};

int main() {

    int x, y, z;
    cin >> x;
    cin >> y;
    cin >> z;
    Sub sub(x, y, z);
    cout << sub.calculate() << endl;

    return 0;
}