'Hello World' of Inheritance (need help)

Hello,
I need to understand the basic syntax of C++ and object oriented design including inheritance. So I'm trying to compile a sort of template to aid my understanding. This code has multiple problems, and I hardly know where to start with all the errors. I was also perplexed when I thought of creating an instance of the most derived object (the truck class) with all the qualities of the base classes; this particular point-of-confusion is that each constructor (as I wrote them) does not set the instance variables for the upper base classes.

Code:

---

# include <stdio.h>
# include <stdlib.h>


class Automobile{
        protected:        /* protected means only derived classes can use directly */
                int a;
                int b;
        public:
                Automobile(int a_, int b_){
                        a = a_;
                        b = b_;
                }
};

Class Truck : Automobile{
        protected:
                int c;
                int d;
        public:
                Truck(int c_, int d_){
                        c = c_;
                        d = d_;
                }
};
       
Class PickUp : Truck{
        private:
                int e;
                int f;
        public:
                PickUp(int e_, int f_){
                        e = e_;
                        f = f_;
                }
};

PickUp::print(){
        printf("%d %d %d %d %d %d", a,b,c,d,e,f);
}
               
int main(){
        PickUp x(?????);
        //I don't understand how to declare a new PickUp object with a,b,c,d,e,f
       
        x.print();
}

---

Thanks in advance.

If you want a constructor to take 6 arguments, then you'll need to declare with that many arguments. Then, using the initialization list, you can forward arguments to the parent's constructor.

There are also other errors, like needing to use public for normal "is-a" inheritance (or the protected members of the grand-parent class will still be unavailable.

Code:

---

# include <stdio.h>
# include <stdlib.h>


class Automobile
{
    protected:        /* protected means only derived classes can directly use */
        int a;
        int b;
    public:
        Automobile(int a_, int b_)
        {
            a = a_;
            b = b_;
        }
};

class Truck : public Automobile  //use public inheritance, or Automobile's a and b won't be accessible to classes derived from this
{
    protected:
        int c;
        int d;
    public:
        Truck(int a_, int b_, int c_, int d_):
            Automobile(a_, b_) //invoke parent constructor with arguments
        {
            c = c_;
            d = d_;
        }
};

class PickUp : public Truck  //use public inheritance
{
    private:
        int e;
        int f;
    public:
        PickUp(int a_, int b_, int c_, int d_, int e_, int f_):
            Truck(a_, b_, c_, d_) //invoke its constructor
        {
            e = e_;
            f = f_;
        }

        void print(); //needs to be declared
};

void PickUp::print() //has return type
{
        printf("%d %d %d %d %d %d", a,b,c,d,e,f);
}

int main()
{
    PickUp x(1, 2, 3, 4, 5, 6);
    x.print();
}

---

Great! Thanks anon, that makes perfect sense too.

The print member function should also be const since it does not modify the object:

Code:

---

class PickUp : public Truck  //use public inheritance
{
...
void print() const;
};

void Pickup::print() const
{
    printf("%d %d %d %d %d %d", a,b,c,d,e,f);
}

---