Page 92 - DCAP404 _Object Oriented Programming

Unit 4: Classes and Objects

num1; Notes
num2 = 3;
int sum = num1 + num2;
return sum;
}
};
int main()

{
Calculator obj;
obj.num1 = 2;
int result = obj.add();
cout << result;
return 0;
}
The second line in the main function is wrong because at that line, main tries to access (use as
identifier) the private member, num1.

4.5.3 The Protected Access Specifier

If a member of a class is public, it can be accessed by an external function including a derived
class. If a member of a class is private, it cannot be accessed by an external function; even a
derived class cannot access it.
The question is, should a derived class not really be able to access a private member of its base
class (since the derived class and base class are related)? Well, to solve this problem you have
another access specifier called, protected. If a member of a class is protected, it can be accessed by
a derived class, but it cannot be accessed by an external function. It can also be accessed by
members within the class. The following code illustrates how a derived class can access a protected
member of a base class:
#include <iostream>
using namespace std;
class Calculator
{

protected:
int num1;
int num2;
};
class ChildCalculator: public Calculator
{
public:

int add()

LOVELY PROFESSIONAL UNIVERSITY 85