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.