💳 ATM Transaction Management System in C

This is a C-based console application that simulates an ATM system. It supports creating user accounts, balance inquiry, deposits, withdrawals, and viewing the transaction history using linked list data structures.

🛠️ Features

• 🔐 Secure PIN Verification for each transaction.
• 🧑 Multiple Users Support with dynamic account creation via ATM number and PIN.
• 💰 Balance Management through deposit and withdrawal functions.
• 📜 Transaction History using a stack-like singly linked list for each user.
• 🔁 Persistent Session for interacting with multiple users without restarting.
• 🗂️ User Selection by ATM Number to access details and perform operations.

📌 Data Structures

• Doubly Linked List – To manage users (struct node)
• Singly Linked List (Stack Behavior) – To manage individual transaction logs (struct single_node)

📋 Functional Overview

Function	Description
Balance()	Returns the current balance for a user after verifying the PIN.
Deposit()	Adds a deposit amount and updates the transaction log.
Withdraw()	Deducts the withdrawal amount and updates the transaction log.
Last_Transactions()	Displays all past deposits/withdrawals (stack-based view).
newuser_details()	Adds a new user with ATM number and PIN using a doubly linked list.
isalreadyexit()	Checks if a user with the given ATM number already exists.

🧪 Sample Run

START

Enter your ATM\_number\[12 digit] : 123456789012
You need to add your card first to continue.
Enter your pin : 1234
Your account added successfully.

WELCOME SCREEN

# 1.Balance(Enter-1).

# 2.Deposit(Enter-2).

# 3.Withdraw(Enter-3).

# 4.Last Transactions(Enter-4).

# 0.Exit(Enter-0).

Enter the option : 2
Enter the pin(4-digit).
1234
Enter the amount to deposit.
1000
Your Deposit of rupees 1000.000000 is successful.
Your Balance is now : 1000.000000.

💾 How to Compile and Run

1. Clone or download this repository.

2. Compile the code:

gcc atm_system.c -o atm

3. Run the application:

./atm

🧠 Future Enhancements

• Add file handling to save and load users and transaction logs across sessions.
• Add OTP-based verification or biometric authentication.
• Use a database (like SQLite) for scalable persistent storage.

📝 Author

• Developed by Harshit Gupta