Adreeja Ghatak

# wrote a program about factorial
adreeja/factorial.py
import sys

def factorial(n):
    """Iterative factorial: works for n >= 0"""
    if n < 0:
        raise ValueError("Negative numbers do not have factorials.")
    result = 1
    for i in range(2, n + 1):
        result *= i
    return result

def main():
    # Usage:
    #   python factorial.py        -> uses default n = 5
    #   python factorial.py 6      -> calculates factorial(6)
    if len(sys.argv) > 1:
        try:
            n = int(sys.argv[1])
        except ValueError:
            print("Please provide a valid integer. Example: python factorial.py 6")
            return
    else:
        n = 5  # default value for quick demo

    try:
        print(f"Factorial of {n} is {factorial(n)}")
    except ValueError as e:
        print(e)

if __name__ == "__main__":
    main()