Classes & Objects

#include <iostream>
#include <string>
using namespace std;

class Student {
public:                         // accessible from anywhere
    string name;
    int roll;
    double marks[3];

    double average() {          // member function (method)
        return (marks[0] + marks[1] + marks[2]) / 3;
    }
    void print() {
        cout << roll << " " << name << " avg " << average() << endl;
    }
};                              // note the semicolon!

int main() {
    Student s1;                 // create an object
    s1.name = "Asha";
    s1.roll = 7;
    s1.marks[0] = 88; s1.marks[1] = 92; s1.marks[2] = 79;
    s1.print();

    Student s2 = s1;            // copy: s2 has its own data
    s2.name = "Ravi";
    s2.roll = 8;
    s1.print();
    s2.print();
    return 0;
}

7 Asha avg 86.3333
7 Asha avg 86.3333
8 Ravi avg 86.3333

#include <iostream>
using namespace std;

class BankAccount {
private:
    double balance = 0;               // hidden: no one outside can set it to -1000

public:
    void deposit(double amount) {
        if (amount > 0) balance += amount;
    }
    bool withdraw(double amount) {
        if (amount <= 0 || amount > balance) return false;
        balance -= amount;
        return true;
    }
    double getBalance() { return balance; }
};

int main() {
    BankAccount acc;
    acc.deposit(5000);
    cout << "withdraw 7000: " << (acc.withdraw(7000) ? "ok" : "refused") << endl;
    cout << "withdraw 1200: " << (acc.withdraw(1200) ? "ok" : "refused") << endl;
    cout << "balance: " << acc.getBalance() << endl;
    // acc.balance = 1000000;   // error: 'balance' is a private member
    return 0;
}

withdraw 7000: refused
withdraw 1200: ok
balance: 3800

#include <iostream>
using namespace std;

class Rectangle {
    double length, width;
public:
    void set(double l, double w);
    double area();
    double perimeter();
};

void Rectangle::set(double l, double w) { length = l; width = w; }
double Rectangle::area()                { return length * width; }
double Rectangle::perimeter()           { return 2 * (length + width); }

int main() {
    Rectangle r;
    r.set(7, 3);
    cout << "area " << r.area() << ", perimeter " << r.perimeter() << endl;
    return 0;
}

area 21, perimeter 20

#include <iostream>
#include <string>
using namespace std;

class Item {
public:
    string name;
    int qty;
    double price;
    double total() const { return qty * price; }
};

double billTotal(const Item items[], int n) {
    double sum = 0;
    for (int i = 0; i < n; i++) sum += items[i].total();
    return sum;
}

int main() {
    Item cart[3] = {{"Notebook", 4, 45.0}, {"Pen", 10, 12.5}, {"Geometry box", 1, 180.0}};
    for (const Item &it : cart)
        cout << it.name << " x" << it.qty << " = " << it.total() << endl;
    cout << "Bill: Rs " << billTotal(cart, 3) << endl;
    return 0;
}

Notebook x4 = 180
Pen x10 = 125
Geometry box x1 = 180
Bill: Rs 485

#include <iostream>
using namespace std;

class Point {
    int x, y;
public:
    void move(int dx, int dy) { x += dx; y += dy; }
    int getX() { return x; }
};

int main() {
    cout << "sizeof(Point) = " << sizeof(Point) << " bytes (two ints)" << endl;
    return 0;
}

sizeof(Point) = 8 bytes (two ints)