Question

In Exercise 1, displayAnimal uses an Animal reference variable as its parameter. Change your code to make the displayAnimal function anim parameter as an object variable, not a reference variable. Run the code and examine the output. What has changed?

Polymorphic behavior is not possible when an object is passed by value. Even though printClassName is declared virtual, static binding still takes place because anim is not a reference variable or a pointer.

Alternatively we could have used an Animal pointer in the displayClass function. Modify your code to make the animparameter a pointer and verify that it now works as expected. Now use the pointer parameter to call the printClassName member function:

anim->printClassName();

Similarly, pointers to a base class may be assigned the address of a derived class object. Add the statement to dynamically allocate a Dog object and assign its address to an Animal pointer named ptrAnimal. Use the pointer to call the printClassName member function in your main function like this:

   Animal *ptrAnimal = new Dog();
   ptrAnimal->printClassName();

We can create an array of Animal pointers, some of which point to Cat objects and some point to Dog objects. Using a loop we can step through the array testing each element by calling the displayAnimal function. Add this code to create a driver program that tests multiple types of objects:

   // Constant for the size of an array.
   const int NUM_TESTS = 4;

   // tests is an array of Animal pointers.
   // Each element of tests is initialized with the
   // address of a dynamically allocated object.
   Animal *tests[NUM_TESTS] =
   { new Dog(),
       new Cat(),
       new Dog(),
       new Cat()
   };

   // Display the class type for each element in the array.
   for (int count = 0; count < NUM_TESTS; count++)
   {
       cout << "Animal #" << count + 1 << endl;
       displayAnimal(tests[count]);
       cout << endl;
   }

================================================================================================

#include

#include

using namespace std;

// Animal is a base class.

class Animal

{

public:

// Constructor

Animal()

{ }

virtual void printClassName() const

{

cout << "Animal";

}

};

// The Dog class is derived from Animal

class Dog : public Animal

{

public:

// Constructor

Dog()

{ }

void printClassName() const

{

cout << "Dog";

}

};

// The Cat class is derived from Animal

class Cat : public Animal

{

public:

// Constructor

Cat()

{ }

void printClassName() const

{

cout << "Cat";

}

};

//*************************************************

// displayAnimal function *

//*************************************************

void displayAnimal(Animal &anim)

{

cout << "This animal is a ";

anim.printClassName();

cout << "." << endl;

}

//*************************************************

// main function *

//*************************************************

int main()

{

Cat myCat;

Dog myDog;

cout << "Calling printClassName member functions." << endl;

cout << "Cat: ";

myCat.printClassName();

cout << endl << "Dog: ";

myDog.printClassName();

cout << endl << endl << "Using function displayClass:" << endl;

displayAnimal(myCat);

displayAnimal(myDog);

system("PAUSE");

return 0;

}

Answer 1

If you have any doubts, please give me comment...

#include <iostream>

#include <string>

using namespace std;

// Animal is a base class.

class Animal {

public:

// Constructor

Animal() {}

virtual void printClassName() const { cout << "Animal"; }

};

// The Dog class is derived from Animal

class Dog : public Animal {

public:

// Constructor

Dog() {}

void printClassName() const { cout << "Dog"; }

};

// The Cat class is derived from Animal

class Cat : public Animal {

public:

// Constructor

Cat() {}

void printClassName() const { cout << "Cat"; }

};

//*************************************************

// displayAnimal function *

//*************************************************

void displayAnimal(Animal *anim) {

cout << "This animal is a ";

anim->printClassName();

cout << "." << endl;

}

//*************************************************

// main function *

//*************************************************

int main() {

// Constant for the size of an array.

const int NUM_TESTS = 4;

// tests is an array of Animal pointers.

// Each element of tests is initialized with the

// address of a dynamically allocated object.

Animal *tests[NUM_TESTS] = {new Dog(), new Cat(), new Dog(), new Cat()};

// Display the class type for each element in the array.

for (int count = 0; count < NUM_TESTS; count++) {

cout << "Animal #" << count + 1 << endl;

displayAnimal(tests[count]);

cout << endl;

}

return 0;

}