A simple C-based ATM simulation system that securely handles account management, PIN hashing using SHA-256, and SMS notifications via Twilio. It supports basic banking operations like withdrawals, deposits, transfers, and balance checks. All account data is stored in files for easy management and testing.

• Create accounts with hashed PINs
• Withdraw, deposit, and check balances
• Transfer funds and pay bills
• Send SMS notifications using Twilio API
• Generate transaction receipts

1. Copy config.example.h to config.h:

   cp config.example.h config.h

2. Open config.h and fill in your actual Twilio credentials:

   #define ACCOUNT_SID "YOUR_TWILIO_ACCOUNT_SID"
   #define AUTH_TOKEN  "YOUR_TWILIO_AUTH_TOKEN"
   #define TWILIO_PHONE_NUMBER "+1YOUR_TWILIO_NUMBER"
   #define USER_PHONE_NUMBER "+91YOUR_NUMBER" 

Make sure the libcurl development package is installed:

# Ubuntu/Debian
sudo apt update
sudo apt install libcurl4-openssl-dev

Compile using:

gcc atm.c -o atm_simulator -lcurl
./atm_simulator