In-Class Exercise
Member Functions and Privacy
This exercise hides the data members and
provides access to them through public member functions.
Given Information
The following code is a solution to the Handout on
Basic Concepts.
Client Module
h1.h
// Basic Concepts
// h1.h
#define NO_TRANSACTIONS 3
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h1.cpp
// Basic Concepts
// h1.cpp
#include "h1.h"
#include "Transaction.h"
int main() {
Transaction tr;
for (int i = 0; i < NO_TRANSACTIONS; i++) {
enter(tr);
display(tr);
}
}
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Transaction Module
Transaction.h
// Basic Concepts
// Transaction.h
struct Transaction {
int acct;
char type;
double amount;
};
void enter(Transaction& tr);
void display(const Transaction& tr);
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Transaction.cpp
// Basic Concepts
// Transaction.cpp
#include <iostream>
using namespace std;
#include "Transaction.h"
void enter(Transaction& tr) {
cout << "Enter the account number : ";
cin >> tr.acct;
cout << "Enter the account type (d for debit, c for credit) : ";
cin >> tr.type;
cout << "Enter the account amount : ";
cin >> tr.amount;
}
void display(const Transaction& tr) {
cout << "Account " << tr.acct;
cout << ((tr.type == 'd') ? " Debit $" : " Credit $") << tr.amount;
cout << endl;
}
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Your Task
Convert the global functions into public member functions and the global calls into
calls on Transaction objects.
Transaction Module
Transaction.h
The header file for your Transaction
module identifies the enter() and
display() functions as public member functions
and the data members as private.
Update your definition of a Transaction:
- convert the global enter() and display()
functions into public member functions
- identify the data members as private
// Member Functions and Privacy
// Transaction.h
struct Transaction {
int acct;
char type;
double amount;
};
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Transaction.cpp
The implementation file for the Transaction module
contains the definitions of the two member functions.
- complete the function headers
- refer to the data members directly
// Member Functions and Privacy
// Transaction.cpp
#include <iostream>
using namespace std;
#include "Transaction.h"
void {
cout << "Enter the account number : ";
cin >> ;
cout << "Enter the account type (d for debit, c for credit) : ";
cin >> ;
cout << "Enter the account amount : ";
cin >> ;
}
void {
cout << "Account " << ;
cout << (( == 'd') ? " Debit $" : " Credit $") << ;
cout << endl;
}
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Client Module
The client program now calls member functions
on the Transaction object:
- replace the global function calls with calls to the member functions
// Member Functions and Privacy
// h2.cpp
#include "h2.h"
#include "Transaction.h"
int main( ) {
Transaction tr;
for (int i = 0; i < NO_TRANSACTIONS; i++) {
}
}
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Note on Encapsulation
In this example the calls to the member functions
have no arguments. The internal aspects of each Transaction are completely hidden from the
client module. This is one aspect of encapsulation.
We can change the names and the order of the data members within
the Transaction module without having to modify any code within
any client module.
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