Functions

Name a block of code

• A function is named code you can use again and again.
• Make one with def name(): and an indented body.
• "Calling" the function by its name runs that code.

Give it inputs (parameters)

• The names in the brackets are parameters — the function's inputs.
• When you call it, you pass in arguments (the real values).
• A function can take more than one parameter.

def shout(word):
    print(word.upper() + "!")

shout("hello")

Send back a result (return)

• return sends a value back to whoever called the function.
• You can store that value or use it in an expression.
• return also ends the function straight away.

def double(x):
    return x * 2

result = double(5)
print(result)

return vs print

• print only shows something on the screen.
• return gives a value back that the rest of your code can use.
• A function with no return gives back None.

In Cambridge pseudocode

• A FUNCTION returns a value; a PROCEDURE just does an action.

FUNCTION Add(A : INTEGER, B : INTEGER) RETURNS INTEGER
    RETURN A + B
ENDFUNCTION

PROCEDURE Greet(Name : STRING)
    OUTPUT "Hello, ", Name
ENDPROCEDURE

Common mistakes

• A function returns None unless you write return; printing is not the same as returning.
• Run a function with (): greet(), not greet.
• Define a function before you call it.

Now you try

• Define each function, then the checks will call it for you.
• Use return to send the answer back (do not print it).