The Supermarket Inventory & Billing Management System is a C-based software solution designed to simplify and automate the essential operations of small and medium retail stores. Traditional supermarket systems rely heavily on manual bookkeeping or complex, database-driven applications that are either inefficient or costly for smaller setups. This project bridges that gap by providing a lightweight, standalone application that efficiently manages inventory, billing, and sales reporting using fundamental programming concepts such as structures, arrays, file handling, and modular design in the C language. The primary goal of this project is to ensure accuracy, automation, and ease of use in everyday supermarket operations. The system allows administrators to manage items — including adding, editing, and viewing product details such as ID, name, price, and stock quantity — while automatically updating inventory levels after each sale. Customers can view available products, generate itemized bills with tax and discount calculations, and enjoy an engaging “Spin-the-Wheel” reward feature that offers random discounts or rewards, improving the user experience. All transactional data and item records are stored persistently in text files, ensuring reliability even after program closure. Key features of the system include: • Automation of billing and stock management to reduce manual workload. • Accurate and error-free transactions with real-time stock updates. • File-based data storage, removing the need for complex databases. • User-friendly console interface, accessible to both admins and customers. • Scalability, allowing future upgrades such as barcode integration or GUI implementation. The project’s development follows a systematic approach involving analysis, design, implementation, and validation, ensuring clarity of code and efficiency in operation. The bibliometric and literature reviews support the project’s design choice, confirming that file-based C programs remain effective educational and practical tools for small-scale automation.