while validheight == False:
        height = float(input("Enter the desired height of the lighthouse (in metres): "))
        if height <= 0 or height >= 1000:
            print("Enter a valid height.")
        else:
            validheight = True
    while validdf == False:
        df = float(input("Enter the desired diameter of the bottom of the lighthouse (in metres): "))
        if df <= 0 or df >= 1000:
            print("Enter a valid diameter for the base.")
        else:
            validdf = True