Unit 1: Introduction to OOP and classes

In procedural programming (C), a program is a list of functions working on shared data. As programs grow, any function can change any data, which makes them hard to maintain. OOP solves this by combining data and functions into objects and controlling access to the data.

• Reusability through inheritance — write once, extend many times.
• Data security through encapsulation and data hiding.
• Easier maintenance and modelling of real-world entities (Student, Account, Car).
• Extensibility — new features can be added with little change to existing code.

• C++ is largely a superset of C — most C programs compile as C++ — and adds references, function overloading, default arguments and bool.

cpp#include <iostream>        // header for input/output
using namespace std;       // use names like cout directly

class Greeting {           // class definition
public:
    void show() { cout << "Welcome to SBS" << endl; }
};

int main() {               // execution starts here
    Greeting g;            // object
    g.show();
    return 0;
}

• cout << (insertion operator) prints; cin >> (extraction operator) reads input.
• endl or "\n" ends a line.
• A typical program has: include files, class declarations, member function definitions, and the main function.

• In C++ a struct can contain member functions and access specifiers; members are public by default (in a class they are private by default).
• Unions share memory among members; C++ unions can have member functions; anonymous unions allow direct member access.

cppstruct Point {
    int x, y;
    void show() { std::cout << "(" << x << ", " << y << ")\n"; }
};

A class has data members (variables) and member functions (methods). Member functions can be defined inside the class or outside using the scope resolution operator ::.

cppclass Account {
private:
    int number;
    double balance;
public:
    void deposit(double amt);            // declared here
    void show() { cout << number << " " << balance; }
};
void Account::deposit(double amt) {      // defined outside
    balance += amt;
}

Objects are declared like variables: Account a1, a2; and members are accessed with the dot operator: a1.show();.

Keeping data private and providing public functions to use it is called data hiding.