B2.3.4 Construct functions and modularization.

--> Time: 45 minutes. Work in pairs, one laptop per pair. <-- 

STAGE 1 - READ (10 min)

Open the FAQ entry "B2.3.4 Construct functions and modularization"
on faq.computersciencewiki.org. Read sections 1 and 3 only
(Functions, and The Principle of Scope). Skip the Java examples.

Copy this into your notebook and fill in the blanks from the reading:

1. A function is a named block of code that performs a ______ task.
2. The inputs to a function are called ______.
3. The word for sending a value back out of a function is ______.
4. A variable created inside a function is ______ to that function,
   which means code outside cannot see it.

STAGE 2 - PREDICT (10 min)

Laptops CLOSED. Write down what each one prints. Then open your
laptop and run them to check.

A)  def double(number):
        return number * 2

    print(double(5))

B)  def shout(word):
        print(word.upper())

    result = shout("hi")
    print(result)

C)  def add(a, b):
        return a + b

    print(add(2, 3) + add(10, 1))

D)  name = "Sam"

    def show():
        print(name)

    show()

STAGE 3 - BUILD (20 min)

Make a new file called my_functions.py. Write these four functions.
Each one is one or two lines. Run the file after EACH function
so you catch mistakes early.

1. greet(name)
   Takes a name. Returns "Hello Ana!" when given "Ana".

2. double(number)
   Takes a number. Returns that number times 2.

3. area(width, height)
   Takes two numbers. Returns width times height.

4. is_long(word)
   Takes a word. Returns True if it is longer than 5 letters,
   otherwise False.

Now add these lines at the bottom and run the file.
You should see exactly the output shown on the right:

    print(greet("Ana"))      ->  Hello Ana!
    print(double(7))         ->  14
    print(area(3, 4))        ->  12
    print(is_long("banana")) ->  True
    print(is_long("cat"))    ->  False

Two rules:
 - Every function must use return, not print.
 - Do not write any function longer than two lines.

STUCK? Here is the shape every one of them follows:

    def name_of_function(input):
        return something

STAGE 4 - EXIT TICKET (5 min)

Answer on paper and hand in:

1. You wrote double(number). Show the line of code you would write
   to double the number 30 and store the answer in a variable
   called big.

2. Why is it better to write double() once and call it five times,
   instead of writing number * 2 in five different places?

3. Look at your area() function. Why does it need two parameters
   when greet() only needs one?

IF YOU FINISH EARLY

Add a fifth function called triple(number) that returns the number
times 3. Then write one line that uses double() and triple()
together on the same number and prints the total.