Unit 1: OOP implementation in C++

A reference variable is an alias for an existing variable. Passing by reference lets a function change the caller's variables without pointers.

cppvoid swap(int &a, int &b) {
    int t = a; a = b; b = t;
}
int main() {
    int x = 5, y = 9;
    swap(x, y);
    cout << x << " " << y;   // 9 5
}

cppclass Account {
    string name; int number; double balance;
public:
    void open(string n, int no, double b) { name = n; number = no; balance = b; }
    void deposit(double a) { balance += a; }
    void withdraw(double a) {
        if (a > balance) cout << "Insufficient balance\n";
        else balance -= a;
    }
    void display() { cout << number << " " << name << " " << balance << "\n"; }
};
Account acc[3];   // array of objects for multiple customers

Overload area() for (base, height) using ½ × b × h and for three sides using Heron's formula, s = (a + b + c)/2 and area = √[s(s − a)(s − b)(s − c)].

• Publication → Book and Tape (hierarchical): the base stores title and price; each derived class adds its own data and a display function.
• Student → Exam → Result (multilevel): Student stores roll number, Exam stores marks and Result calculates and displays the total.

• Unary operator: overload - to negate the coordinates of a point: void operator-() { x = -x; y = -y; }
• Binary operator: overload + to add two complex numbers or two distances.
• Virtual function: a base Shape with virtual void area(); derived Circle and Rectangle override it; call through Shape *.
• Abstract class: make area() pure virtual (= 0) and show that Shape objects cannot be created.
• Files: write student records with ofstream, read them with ifstream, and copy a file with get() and put().