Day 45: Introduction to OOPs (Part 2)

📅 Date: Feb 14, 2026

🧠 Mood: Security Guard 👮‍♂️

🔥 Topic: OOPs Part 2: Access Modifiers & Encapsulation

🛑 The Problem with "Public"

Yesterday, we made everything public:. It was easy, but dangerous.

Imagine a Bank Account class. If the balance is public, anyone can do this:

Account myAcc;
myAcc.balance = -500000; // ❌ Hacked! Balance can't be negative.
myAcc.balance = 9999999; // ❌ Fraud! Anyone can change money.

This is why we need Access Modifiers. We need to hide sensitive data.

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🔐 Access Modifiers: The Security Guards

C++ provides 3 levels of security:

1. Private 🔒 (Default)

Only code inside the class can access it. No one from main() can touch it. (Like a Bank Vault).

2. Public 📢

Accessible from everywhere. (Like the Bank Counter).

3. Protected 🛡️

Used in Inheritance (We will cover this in Day 46). Similar to Private but shared with children classes.

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🛠️ Getters & Setters (Encapsulation)

If data is private, how do we use it?
We create public functions to access them securely. This concept is called Encapsulation (wrapping data and methods together).

• Setter: A function to SET values (with validation check).
• Getter: A function to GET (read) values.

💻 The Secure Bank Code

#include <iostream>
using namespace std;

class BankAccount {
    // Data is hidden (Private)
    private: 
        int balance; 

    public:
        // SETTER (Write Access with Security)
        void setBalance(int amount) {
            if(amount < 0) {
                cout << "❌ Error: Balance cannot be negative!" << endl;
            } else {
                balance = amount;
                cout << "✅ Balance Updated!" << endl;
            }
        }

        // GETTER (Read Access)
        int getBalance() {
            return balance;
        }
};

int main() {
    BankAccount myAcc;
    
    // myAcc.balance = 5000; // ❌ ERROR! Private property.

    // Correct way: Use Setter
    myAcc.setBalance(-500); // Output: Error: Balance cannot be negative!
    myAcc.setBalance(1000); // Output: Balance Updated!

    // Correct way: Use Getter
    cout << "My Balance is: " << myAcc.getBalance();
    
    return 0;
}

💡 Key Takeaway: We didn't allow direct access. We forced the user to go through setBalance(), where we added an if condition to check for valid input. This is Data Hiding.

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🚀 Day 45 Challenge

Create a class Student.

1. Make age a private variable.
2. Create a setAge(int a) function.
3. Inside Setter, check if age is less than 0 or greater than 100. If yes, print "Invalid Age".
4. In main(), try to set age as 150 and see what happens.

Next Up: Day 46 - Constructors & Destructors (The Life Cycle).