Unit 1: OOP implementation in C++

cpp#include <iostream>
using namespace std;
struct S { int a; };                 // members public by default
union U { int i; float f; };          // members share memory
class C { int x; public: void set(int v) { x = v; } int get() { return x; } };
int main() {
    S s{5}; U u; u.i = 10; C c; c.set(7);
    cout << s.a << " " << u.i << " " << c.get() << " " << sizeof(U) << endl;
}

cppclass Student {
    static int count;
    int marks;
public:
    Student(int m) : marks(m) { ++count; }
    inline int getMarks() const { return marks; }
    static int total() { return count; }
    friend void compare(const Student &a, const Student &b);
};
int Student::count = 0;
void compare(const Student &a, const Student &b) {
    cout << (a.marks > b.marks ? "First" : "Second") << " is higher\n";
}

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

cppclass Box {
    int l, b;
public:
    Box() : l(1), b(1) { cout << "Default\n"; }
    Box(int x, int y) : l(x), b(y) { cout << "Parameterised\n"; }
    Box(const Box &o) : l(o.l), b(o.b) { cout << "Copy\n"; }
    ~Box() { cout << "Destructor\n"; }
    int area() { return l * b; }
};
int main() { Box a; Box b(3, 4); Box c = b; cout << c.area() << endl; }

• Viva: constructors have the class name and no return type; destructors run in reverse order of creation.

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().