Enhance README with usage and operations

README.md

@@ -1,21 +1,48 @@
-
 # Scientific Calculator
 
-A simple scientific calculator built in Python.
+An interactive **command-line** scientific calculator written in Python. It presents a numbered menu, reads your inputs, and prints results for each operation. The core math lives in small functions in `calculator.py`, so you can also import them from another script if you want to reuse the same behavior.
 
-## Features
-- Basic arithmetic operations
-- Trigonometric functions
-- Logarithms and exponentials
+## What it does
+
+- Runs a **REPL-style loop**: choose an operation, enter operands, see `Result: …`, repeat until you exit.
+- Uses only the **Python standard library** (`math`); no extra packages to install.
+- **Validates** some edge cases: division by zero and logarithms of non-positive numbers raise clear errors instead of failing silently.
+
+## Operations
+
+| Choice | Operation | Inputs | Notes |
+|--------|-----------|--------|--------|
+| 1 | Add | `x`, `y` | |
+| 2 | Subtract | `x`, `y` | |
+| 3 | Multiply | `x`, `y` | |
+| 4 | Divide | `x`, `y` | Error if `y` is zero |
+| 5 | Sine | `x` | `x` is in **radians** |
+| 6 | Cosine | `x` | **radians** |
+| 7 | Tangent | `x` | **radians** |
+| 8 | Logarithm | `x`, optional base | `x` must be **> 0**; base defaults to **e** if you press Enter |
+| 9 | Exponent | `x`, `y` | `x` to the power `y` (`math.pow`) |
+| 0 | Exit | — | Ends the program |
+
+Invalid menu choices print `Invalid choice.` Other problems (bad numeric input, domain errors) print `Error: …` with the exception message.
+
+## Requirements
+
+- Python 3 (any recent 3.x is fine)
 
 ## Usage
-1. Run the calculator:
-   ```
+
+From the project directory:
+
+```bash
 python calculator.py
 ```
 
-## Files
-- `calculator.py` — Main calculator script
+Follow the on-screen prompts. For logarithms, leave the base blank to use the natural logarithm (base **e**).
+
+## Project layout
+
+- **`calculator.py`** — Menu-driven `main()` plus the operation functions (`add`, `subtract`, `multiply`, `divide`, `sine`, `cosine`, `tangent`, `logarithm`, `exponent`).
 
 ## Disclaimer
+
 For learning purposes.