...
class Cow {
 public:
    // We can only have a Cow if we know
    // how many spots it has and how old it is
    Cow(int numSpots, int age);
    Cow() = delete;

    // Moo the right number of times.
    void moo(int numMoos) const;

    // Accessor member functions
    int getNumSpots() const;
    int getAge() const;

    // Mutator member functions
    void setNumSpots(int numSpots);
    void setAge(int age);

 private:
    // Per-Cow data
    int numSpots_;
    int age_;
};
...

...
using namespace std;

Cow::Cow(int numSpots, int age)
    : numSpots_{numSpots},
      age_{age}
{
    cout << "Made a cow with " << numSpots_ << " spots!" << endl;
}

void Cow::moo(int numMoos) const {
    for (int i = 0; i < numMoos; ++i) {
        cout << "Moo! ";
    }
    cout << endl;
}

int Cow::getNumSpots() const {
    return numSpots_;
}

int Cow::getAge() const {
    return age_;
}

void Cow::setNumSpots(int numSpots) {
    numSpots_ = numSpots;
}

void Cow::setAge(int age) {
    age_ = age;
}

...
using namespace std;

int main() {
    Cow bessie{3, 12};
    const Cow mabel{1, 2};

    // This line wouldn't work!
    // Cow duke;

    bessie.moo(1);
    mabel.moo(2);
    bessie.setAge(4);

    // This line wouldn't work!
    // mabel.setAge(2);

    return 0;
}