Activity 12-1 - Classes: Constructors for Initialization
                      A Class Inside Another Class


In your previous lab, you have used a function set to initialize the values of the data members inside the class. C++ includes special provisions for such initialization. While it is not an error to include a set function in a class, the standard way to initialize the data members of a class usually is NOT done by adding a set member function but rather using a special kind of member function called a constructor that is automatically called when an object of the class is declared.  The constructor initializes the values of member variables and can do any other initialization that may be needed. A class can have many constructors.

Here are two things you need to remember when you work with constructors:

    1) A constructor MUST have the same name as the class.  The constructor for class Loan is called Loan.

    2) A constructor DOES NOT have a type, thus it CANNOT return a value.

In the Loan class, the set function can be replaced with the constructor as its job is to initialize the variable members of the class.

Here is the P12.1a.cpp program with constructors.

// P12.1a.cpp - This program is a driver written to demonstrate how the constructor function works.
#include<iostream>

class Loan  // Loan is called structure tag
{
    public:
         Loan( );
         Loan(int ID, float amount, float rate, int term);
         void set( );
         float payment( );
         void display( );
   private:
       int ID;  // assume an unique integer between 1111-9999
       float amount; // $ amount of the loan
      float rate; // annual interest rate
      int term;  // number of months, length of the loan
 };

int main( )
{
    Loan loan1(1234, 2300, 5.5, 410);  // initialize to values given
    Loan loan2;  // use the default values
    Loan loan3;
    Loan loan4 = loan1;

    cout << "Display loan1 \n";
    loan1.display();

    cout << "Display loan2 \n";
    loan2.display();

    cout << "Display loan4 \n";
    loan4.display();

    loan3.set( ); // set the values
    cout << "Display loan3 \n";
    loan3.display();

    return 0;
}

Loan::Loan( )
{
// Constructor 1:
// Body intentionally kept empty so the default values are used.
// If you wish to set the default value of the members to specific
// values, here is the place to do it.
// For example, to make the default value of amount = 0
// you will use amount = 0;

// You could actually copy the body of set function here too
}

Loan::Loan(int I, float am, float rt, int trm)
{

// Constructor 2:
// This constructor sets the values of the members to specific
// values that are passes by value in the parameters.

      ID = I;
      amount = am;
      rate = rt;
      term = trm;
}

void Loan::set( )
{
       // Initialize the loan1 object
      cout << "Enter the ID of this loan \n";
      cin >> ID;

      cout << "Enter the amount of this loan \n";
      cin >> amount;

      cout << "Enter the annual interest rate of this loan (in %) \n";
      cin >> rate;

      cout << "Enter the term (number of months, length of the loan) \n";
      cin >> term;
}

void Loan::display()
{
     cout << ID << endl;
     cout << amount << endl;
     cout << rate << endl;
     cout << term << endl;
}

Exercise 12.1
Modify the above program to include at least 2 constructors. Write a driver that creates 2 loans, prints the loans and the payment due. Use the newly defined constructors. Call the program ex121.cpp.