# This function adds two numbers
def add(x, y):
    return x + y

# This function subtracts two numbers
def subtract(x, y):
    return x - y

# This function multiplies two numbers
def multiply(x, y):
    return x * y

# This function divides two numbers
def divide(x, y):
    return x / y

def avg(x, y):
    return (x + y) / 2

def sci(x, y):
    return x * 10 ** y


print("Select operation.")
print("1.Add")
print("2.Subtract")
print("3.Multiply")
print("4.Divide")
print("5.Average")
print("6.Scientific Notation")

while True:
    # take input from the user
    choice = input("Enter choice(1/2/3/4/5/6): ")

    # check if choice is one of the four options
    if choice in ('1', '2', '3', '4', '5', '6'):
        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 == '1':
            print(num1, "+", num2, "=", add(num1, num2))

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

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

        elif choice == '4':
            print(num1, "/", num2, "=", divide(num1, num2))

        elif choice == '5':
            print(f"avg({num1}, {num2})", "=", avg(num1, num2))

        elif choice == '6':
            print(f"{num1}e{num2}", "=", sci(num1, num2))
        
        # check if user wants another calculation
        # break the while loop if answer is no
        next_calculation = input("Let's do next calculation? (yes/no): ")
        if next_calculation.lower().startswith('n'):
          break
    else:
        print("Invalid Input")