Do I need to initiate parent class or just child class - c++

Question

I am new in programing and I am analyzing code with parent class fruit and child classes apple and pear. In this example there is pointer to parent class. After I extended this code I find out that using object I can access parent public members and all child members. Question is why do I need those pointers?
// are this pointer needed since I can use j.setWeight(11)
#include <iostream>
using namespace std;
class fruit {
private:
int weight;
public:
void setWeight(int x)
{
weight = x;
}
int getWeight()
{
return weight;
}
};
class apple : public fruit {
public:
void eat()
{
cout << "Now I am eating apple"
<< "=" << getWeight() << endl;
}
};
class pear : public fruit {
public:
void eat()
{
cout << "Now I am eating pear"
<< " = " << getWeight() << endl;
}
};
int main()
{
apple j;
pear k;
fruit* fruit1 = &j;
fruit* fruit2 = &k;
k.setWeight(5);
k.eat();
fruit1->setWeight(11);
apple apple;
apple.postaviTezinu(16);
apple.jelo();
return 0;
}
are this pointers needed since I can use j.setWeight(11) and results is same as
fruit1 -> setWeight(11) ... what s difference, thx

Answer 1

I suspect that the code you are looking at was written to demonstrate how pointers to base classes can be used with objects of derived classes. No, pointers are not necessary for the functionality of this learning exercise. In fact, that is probably the reason this functionality was chosen. Since you see how to accomplish the same thing without pointers, it should be easier for you to relate pointers to what you already know.
The key learning points I see in this exercise are
The same pointer type (fruit *) can point to objects of different types (apple or pear).
When using the pointer to the base class, you can access base class members.
When using the pointer to the base class, you cannot access derived class members. (Implied by omission; compare what is done with k to what is done with fruit1.)
You will need to move on to the more advanced lessons to learn when pointers are more useful than accessing objects directly (probably after eat() is turned into a virtual function). For now, just learn how the same task can be accomplished by different means.
(Sure, you could get that information here, but that code looks like it's part of a series. Continuing with that series might be the better way to learn.)

Answer 2

Since you're new to programming, learning polymorphism may be a bit advanced for you at this stage. To answer your question directly: No, you don't need pointers in your example code, and they are in no way helpful.
However, pointers to objects are often useful for:
Reducing unnecessary copying of objects
In the case of polymorphism (as in your example) pointers help in sections of your programme where you don't know which object type you're dealing with, or don't want to have to deal with them in different ways
Example:
#include <iostream>
#include <vector>
class A
{
public:
virtual void foo ()
{
std::cout << " I am A\n";
}
};
class B : public A
{
public:
virtual void foo ()
{
std::cout << " I am B\n";
}
};
void bar ( const std::vector <A*> & obj )
{
// Here it outputs the foo () function that is
// appropriate for the class
for ( unsigned int i = 0; i < obj . size (); ++i )
obj [i] -> foo ();
}
int main ()
{
A a1, a2, a3;
B b1, b2, b3;
// the below input style requires C++11,
// otherwise input them one-by-one
std::vector <A*> array {&a1, &b1, &a2, &a3, &b2, &b3};
bar ( array );
return 0;
}
The above array can store any A objects, including the inherited objects (it can't do this without pointers); and the bar function can still perform operations on the elements in the array without needing to know which object type they belong to within the inheritance tree (due to the virtual function). This is crucial for taking advantage of polymorphism, and saving on repetition of functions and code in general.