def say_hello():
    print('Hello World!')


def area_of_square(length):
    return length**2


def area_of_circle(radius):
    pi = 3.1415926
    return pi*radius**2

# pi can also be defined outside of the function
# good and bad?
# what if someone change the value outside?


def area_of_rectangle(length,width):
    return length*width



def app():
    age = int(input('What\'s your age?'))
    print('Your age is {}'.format(age))
    print('-------')
    app()

app()