Functions

When the same piece of a program is needed in several places, you give it a name. A named piece like that is called a function.

Give a block a name

function starts the description: a name, and in the brackets the parameters, the values the function will be given when it is called. The indented lines are its body. On its own the body does not run: it waits to be called.

function greet(name):
    say("Hi, " + name + "!")

greet("Olya")
greet("Taras")

Hi, Olya!
Hi, Taras!

Return an answer

A function can do more than print: it can hand a value back. That is what return does.

function area(width, height):
    return width * height

say("The room's area:", area(4, 3))

The room's area: 12

After return the function ends at once, even when more lines follow.

A function can call itself

A function may call itself inside its own body. What matters is that there is a case where it stops calling and simply returns an answer.

function factorial(n):
    if n <= 1:
        return 1
    return n * factorial(n - 1)

say("5! =", factorial(5))

5! = 120

Try it yourself

1. Write a function that returns the smaller of two numbers.

function smaller(a, b):
    if a < b:
        return a
    return b

say(smaller(9, 4))

4

2. Write a function that prints a word a given number of times.

function repeat_word(word, times_to_say):
    repeat times_to_say times:
        say(word)

repeat_word("Yu", 3)

Yu
Yu
Yu