def calc():
    print("Select operation.")
    print("1.Add")
    print("2.Subtract")
    print("3.Multiply")
    print("4.Divide")

    while True:
        choice = input("Enter choice(1/2/3/4): ")

        if choice in ('1', '2', '3', '4'):
            num1 = float(input("Enter first number: "))
            num2 = float(input("Enter second number: "))

            if choice == '1':
                print(num1, "+", num2, "=", num1+num2)

            elif choice == '2':
                print(num1, "-", num2, "=", num1-num2)

            elif choice == '3':
                print(num1, "*", num2, "=", num1*num2)

            elif choice == '4':
                print(num1, "/", num2, "=", num1/num2)
            break
        else:
            print("Invalid Input")

