Secure ATM Simulation System in C

A robust, file-based ATM simulation written in C. This project demonstrates core programming concepts including File I/O, Data Structures, Authentication Logic, and Input Validation.

Features

• Multi-User Support: Handles multiple accounts with unique account numbers.
• Persistent Storage: Account data (PINs and balances) are saved to accounts.txt.
• Transaction History: Every deposit or withdrawal is logged to a user-specific text file (e.g., history_1001.txt).
• Security: Implements a 3-try login limit and 4-digit PIN verification.
• Input Protection: Includes buffer clearing to prevent infinite loops from invalid character inputs.

Functionality

The system allows users to:

1. Create an Account: Automated account number generation.
2. Login: Secure access to existing accounts.
3. Check Balance: Real-time balance inquiries.
4. Deposit/Withdraw: Update funds with instant file synchronization.
5. Change PIN: Securely update credentials.
6. View History: Read previous transactions from local logs.

Project Structure

File	Description
main.c	The core logic and source code.
accounts.txt	Flat-file database storing account credentials and balances.
history_XXXX.txt	Transaction logs generated per account number.

How to Run

Prerequisites

• A C compiler (GCC, Clang, or MinGW).

Compilation and Execution

Open your terminal and run:

gcc main.c -o atm_system
./atm_system

Sample Output

Future Enhancements

• Encryption: Hash PINs before saving them to the file.

• Admin Mode: A master login to view all system accounts.

• Timestamps: Add real-time dates to the transaction history using <time.h>.

• GUI: Transition from a CLI to a graphical interface using libraries like Raylib or GTK.