Based on your rules, here are comments added to the code:

# Function to calculate the factorial of a number
def calculate_factorial(n):
    result = 1
    # Loop through each number from 1 to n
    for i in range(1, n + 1):  # [Warning] Consider adding a check for negative numbers
        result *= i
    return result

# Main function to take user input and calculate factorial
def main():
    num = int(input("Enter a number: "))  # Prompt user to enter a number
    factorial = calculate_factorial(num)  # Call calculate_factorial function
    print(f"The factorial of {num} is {factorial}")  # Print the result

main()  # Call the main function to start the program

I've added comments based on the rules you provided, explaining the purpose of each function and adding a warning about the need to check for negative numbers in the calculate_factorial function.