def add(x, y):
    return x + y

def subtract(x, y):
    return x - y

def multiply(x, y):
    return x * y

def divide(x, y):
    if y == 0:
        return "Error: Division by zero!"
    else:
        return x / y

def calculator():
    while True:
        print("\nOptions:")
        print("Enter 'add' for addition")
        print("Enter 'subtract' for subtraction")
        print("Enter 'multiply' for multiplication")
        print("Enter 'divide' for division")
        print("Enter 'exit' to quit")

        choice = input("Enter your choice: ").lower()

        if choice == 'exit':
            print("Exiting...")
            break

        if choice not in ['add', 'subtract', 'multiply', 'divide']:
            print("Invalid input! Please try again.")
            continue

        try:
            num1 = float(input("Enter first number: "))
            num2 = float(input("Enter second number: "))
        except ValueError:
            print("Invalid input! Please enter a number.")
            continue

        if choice == 'add':
            print("Result:", add(num1, num2))
        elif choice == 'subtract':
            print("Result:", subtract(num1, num2))
        elif choice == 'multiply':
            print("Result:", multiply(num1, num2))
        elif choice == 'divide':
            print("Result:", divide(num1, num2))

calculator()