Write a Python program for a simple calculator that performs basic arithmetic operations $($addition$,$ subtraction, multiplication, and division$).$ The program should include the following components :

$$ Separate functions for addition, subtraction, multiplication, and division.

$$ A main calculator function that:

$$ Displays a menu of operations.

$$ Accepts user input for the desired operation.

Takes two numbers as input.

$$ Calls the appropriate function based on the user's choice.

$$ Prints the result.

$*$ Ensure that your program handles invalid inputs and division by zero cases gracefully.

Include comments in your code to explain the purpose of each section