Lab Cycle 1 — Control Flow, Loops & Functions

def is_prime(n):
    # Base cases: numbers <= 1 are not prime
    if n <= 1:
        return False
    # 2 and 3 are prime numbers
    if n <= 3:
        return True
    # Exclude even numbers and multiples of 3
    if n % 2 == 0 or n % 3 == 0:
        return False
    
    # Check factors up to sqrt(n)
    i = 5
    while i * i <= n:
        if n % i == 0 or n % (i + 2) == 0:
            return False
        i += 6
    return True

def main():
    try:
        num = int(input("Enter a positive integer: "))
        if is_prime(num):
            print(f"{num} is a PRIME number.")
        else:
            print(f"{num} is NOT a prime number.")
    except ValueError:
        print("Invalid input! Please enter a valid integer.")

if __name__ == "__main__":
    main()