🏧 ATM Simulator — C++ OOP Project

A console-based ATM and banking system built in C++ demonstrating core Object-Oriented Programming principles — encapsulation, classes, constructors, and file I/O for persistent account storage.

---

🎯 What This Project Does

A fully functional ATM Simulator that models real banking workflows through a menu-driven console interface. Demonstrates clean OOP design with three cooperating classes, secure PIN authentication, and persistent account data stored across sessions using file I/O.

---

✨ Features

• 🔐 PIN-based authentication — secure login before any transaction
• 🏦 Account creation — Bank class creates and persists new accounts
• 💰 Deposit — add funds with input validation
• 💸 Withdrawal — deduct funds with insufficient balance protection
• 📊 Balance inquiry — check current balance instantly
• 🔑 PIN change — update PIN securely mid-session
• 💾 Persistent storage — account data saved to .txt files and reloaded across sessions
• ✅ Input validation — handles invalid amounts and incorrect PINs gracefully
• 📋 Menu-driven UI — clean, looping console interface

---

🏗️ OOP Design

The project is built around 3 well-defined classes that model real-world banking entities:

┌─────────────────────────────────────────────────────┐
│                    Account Class                    │
│  - acc_holder_name, account_num, pin, balance       │
│  - Static counter: next_acc_num (starts at 101)     │
│  + deposit(), withdraw(), authenticate()            │
│  + getBalance(), changePin(), display()             │
│  + saveToFile(), loadFromFile()   ← File I/O        │
└──────────────────────┬──────────────────────────────┘
                       │ uses
          ┌────────────┴────────────┐
          │                         │
┌─────────▼──────────┐   ┌─────────▼──────────┐
│     Bank Class     │   │      ATM Class      │
│  + create_acc()    │   │  + run()            │
│    Creates Account │   │    Loads account    │
│    Saves to file   │   │    Authenticates    │
└────────────────────┘   │    Runs menu loop   │
                         └─────────────────────┘

OOP Concepts Demonstrated

Concept	Where Used
Classes & Objects	Account, Bank, ATM — each models a real entity
Encapsulation	private fields in Account; accessed only via public methods
Constructors	Default constructor + parameterized constructor in Account
Static members	next_acc_num auto-increments account numbers (starts at 101)
File I/O	saveToFile() / loadFromFile() — persistence across program runs
Input Validation	Deposit/withdrawal checks; PIN mismatch handling
Separation of Concerns	Bank creates accounts; ATM handles transactions

---

🗂️ Project Structure

ATM_Simulator-OOPS_Project/
├── ATM_Simulator.cpp    ← Full source code (223 lines)
├── ATM_flowchart.png    ← ATM class flowchart
├── Bank_flowchart.png   ← Bank class flowchart
├── main.png             ← Main function flowchart
└── README.md

Account data is stored as <account_number>.txt files (e.g., 101.txt) created at runtime in the working directory.

---

📊 Flowcharts

Main Function Flow

ATM Class Flow

Bank Class Flow

---

⚡ How to Compile & Run

Prerequisites

• Any C++ compiler: GCC, Clang, or MSVC
• C++11 or newer

Compile with GCC

g++ ATM_Simulator.cpp -o atm_simulator

Run

./atm_simulator        # Linux / Mac
atm_simulator.exe      # Windows

---

🖥️ Sample Session

--------- MENU ---------
1. Create Account
2. Use ATM
3. Exit
Choose option: 1

Enter Customer's name: Kunal
Enter Pin: 1234
Set Initial Balance: 5000
-----Account Created-----
Account Holder's name: Kunal
Account Number: 101
Current balance: 5000

--------- MENU ---------
Choose option: 2

Enter Account Number: 101
Enter PIN: 1234

--------- MENU ---------
1. Check Balance
2. Deposit
3. Withdraw
4. Change PIN
5. Exit
Choose option: 2

Enter deposit amount: 2000
Amount deposited successfully.

Choose option: 1
Current balance: 7000

Choose option: 5
Transaction complete. Thank you!

---

🧠 Key Implementation Details

Static Account Numbering

static int next_acc_num;          // shared across all Account objects
account_num = ++next_acc_num;     // auto-increments from 101

File Persistence

Each account is saved to a uniquely named .txt file, reloaded on next login:

void saveToFile() {
    ofstream file(to_string(account_num) + ".txt");
    file << account_num << endl << pin << endl << balance;
}

PIN Authentication

bool aunthication(int P) {
    return pin == P;    // true only if PIN matches
}

Balance Validation

void withdraw(float amount) {
    if (amount <= 0)           cout << "Invalid amount.\n";
    else if (amount > balance) cout << "Insufficient Funds.\n";
    else balance -= amount;
}

---

🗺️ Possible Extensions

• Multi-account support using vector<Account>
• Transaction history log appended to file per session
• Interest calculation for savings accounts
• Account-to-account transfer
• Masked PIN input using getch()
• SQLite database instead of flat .txt files

---

📚 About

Built as an academic OOP project to demonstrate class design, encapsulation, and file handling in C++.

Developed by Kunal Yadav — B.Tech Computer Science, Manav Rachna University

---

🤝 Connect

• 💼 LinkedIn
• 🐙 GitHub
• 📧 kunalyadav49101@gmail.com

---

⭐ If this helped you understand OOP in C++, consider starring the repo!