"Simple Interest Calculator" Challenge

🌟 **Hello Future Developers!**

**Challenge:** Develop a C program that calculates simple interest based on user-provided values for principal amount, rate of interest, and time. This task will test your understanding of basic arithmetic operations and user input processing.

**Instructions:**

1. Fork this repository.
2. Create a new branch.
3. Write a C program that takes input for principal amount, rate of interest, and time (in years), and calculates and displays the simple interest.
4. Ensure the program handles decimal inputs correctly and provides clear output.
5. Commit your changes and submit a pull request.

**Bonus:** Implement error handling for invalid inputs to provide user-friendly error messages.

**Happy Coding!** 🚀

*Note: This beginner-friendly issue is a great way to practice basic arithmetic operations and user input validation in C!*

No target file or test is named; first inspect the repository for its existing C program layout and entry points. Add the simple-interest calculator with decimal input and clear output, then verify valid values work and, if attempted, invalid inputs receive friendly errors.

索引モデルが issue の本文から書いたものです。