·       Structures and Classes

o      Structures. 

§       A structure is a collection of variables that are referenced under one name

§       Structures provide convenient means of keeping related information together

§       Structures are called compound data types because they consist of several different, yet logically connected, variables

§       An example using a structure in C++ that  involves accessing and mutating the member variables is shown below

 

#include <iostream>

#include <string>

using namespace std;

 

struct Person

{

      string      firstName;

      string      middleName;

      string      lastName;

      string      ssn;

      int         heightInches;

      double      weightPounds;

} Man;

 

 

int main()

{

      Man.firstName = "Joseph";

      Man.middleName = "K.";

      Man.lastName = "Russell";

      Man.ssn = "123-45-6789";

      Man.heightInches = 71;

      Man.weightPounds = 178.5;

 

      cout << Man.firstName << " " << Man.middleName

            << " " << Man.lastName << endl

            << "SSN: " << Man.ssn << endl

            << "Height: " << Man.heightInches

<< " inches\n" << "Weight: "

<< Man.weightPounds << " pounds\n";

 

      cout << "\nENTER NEW INFORMATION\n\n";

      cout << "First Name: ";

      cin >> Man.firstName;

      cout << "Middle Name: ";

      cin >> Man.middleName;

      cout << "Last Name: ";

      cin >> Man.lastName;

      cout << "SSN: ";

      cin >> Man.ssn;

      cout << "Height in inches: ";

      cin >> Man.heightInches;

      cout << "Weight in pounds: ";

      cin >> Man.weightPounds;

 

      cout << "\nTHE NEW INFORMATION\n\n";

 

      cout << Man.firstName << " " << Man.middleName

            << " " << Man.lastName << endl

            << "SSN: " << Man.ssn << endl

            << "Height: " << Man.heightInches

<< " inches\n" << "Weight: "

<< Man.weightPounds << " pounds\n";

 

      return 0;

}

 

                                    // Example Output

 

 

o      Classes. 

§       A class defines a new data type, which can be used to create objects.  For example, the variable named salesman is a Person object in the declaration shown below.

 

Person salesman;

 

§       When a class is defined, the programmer defines both the data and the functions that operate upon that data.  The data is called member data and the functions are called member functions.

§       By default, data and function members of a class are private to that class.  The public keyword is an access specifier that is used to declare the public members of a class.

§       A constructor is a special member function that is invoked when an object is created.  If you do not declare a constructor for a class, the compiler will create a default constructor for you that will create an empty object.

§       If you declare a constructor for a class that takes one or more arguments, you may want to write your own default constructor that takes no arguments because the compiler will not provide a default constructor under these circumstances.

§       Member functions are invoked using the dot operator similar to the way a public member variable would be accessed or changed.

 

// Example

Person student;

student.displayName();

 

§       Only member function prototypes are needed in the definition of a class.

§       Member function definitions outside of the class must include the class name for which they belong.  This is done by using the scope resolution operator (::).  The name preceding the :: is called the type qualifier because it qualifies the function name to one type.

 

// Example

void Person::displayName()

{

     cout << _firstName << “ “

          << _middleName << “ “

          << _lastName << endl;

}

 

o      Revisiting Encapsulation

§       An Abstract Data Type (ADT) is a data type where the programmers do not have access to the details of how the values and operations of the type are implemented.  Example: int, double, and char are ADTs.

§       Implementation pertains to the way in which methods of the class operate on the member variables, i.e., the way in which the variables of the class are manipulated.

§       The Interface is the information a programmer needs to use the class.  This is the programmer’s Application Programmer’s Interface (API) to the class.

§       Encapsulation is accomplished by creating an ADT.  This is done by separating the interface from the implementation.  A good benefit of encapsulation is that you can change the implementation at any time without having to change other parts of your program.

o      Public and Private Members

§       Public members can be referenced by name anyplace without restriction.

§       Private Members can only be referenced by name within the definitions of member functions of the same class or by friends of the class.

 

·       Constructors – A constructor is a special member function that is automatically called when an object of a class is declared.

o      If no constructor is specified by the programmer, the compiler will provide one automatically that will produce an empty object.

o      Constructors can be overloaded.  If you are providing a constructor that takes one or more arguments, you may want to include your own default constructor.

 

// Example

#include <iostream>

#include <string>

using namespace std;

 

class Person

{

public:

      Person();

      Person(string, string, int);

      Person(int);

      void displayName();

      void displayHeight();

private:

      string      _firstName;

      string      _lastName;

      int         _heightInches;

};

 

Person::Person()

{

      cout << "Inside my default constructor.\n";

      _firstName = "John";

      _lastName = "Doe";

      _heightInches = 68;

 

}

 

Person::Person(string firstName, string lastName, int heightInches)

{

      cout << "In constructor that takes all information.\n";

      _firstName = firstName;

      _lastName = lastName;

      _heightInches = heightInches;

}

 

Person::Person(int heightInches)

{

      cout << "In constructor that takes height only.\n";

      _firstName = "Jane";

      _lastName = "Smith";

      _heightInches = heightInches;

}

 

void Person::displayName()

{

      cout << endl << _firstName << " " << _lastName << endl;

}

 

void Person::displayHeight()

{

      cout << "Height = " << _heightInches << " inches.\n";

}

 

int main()

{

      Person A, B("Joseph", "Russell", 71), C(70), D(B);

 

      A.displayName();

      A.displayHeight();

     

      B.displayName();

      B.displayHeight();

     

      C.displayName();

      C.displayHeight();

     

      D.displayName();

      D.displayHeight();

 

      return 0;

}

 

// Output for the above program

 

·       Initialization Section – An initialization section goes after the parenthesis that ends the parameter list and before the opening brace of the function body

 

// Example

      Person::Person(int heightInches) : _heightInches(heightInches)

      {

            if(_heightInches > 72)

                  cout << "The person is over six feet tall.\n";

            else

                  cout << "The person is less than six feet tall.\n";

      }    

 

     // Replacing the constructor in the above program

          // yields the following output:

 

 

·       Review the Display 7.2 Example in the book beginning on page 269.