Develop a command-line calculator application to perform basic arithmetic operations.
- Initialize a Python project and set up a virtual environment.
- Implement functions for:
- Addition
- Subtraction
- Multiplication
- Division
- Use a loop to allow continuous calculations until the user decides to exit.
- Handle invalid input and division by zero errors.
- Test the calculator with various inputs to ensure accuracy.
- Provide a usage guide and example inputs.
- Make a simple UI using Flask or Gradio.
